diff --git a/.gitignore b/.gitignore
index df3f117..7f4b781 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 /phpunit.xml
 /composer.lock
+.php_cs.cache
 *.phar
 /vendor/
 /bin/
diff --git a/.php_cs b/.php_cs
index b851ebc..6b5bddd 100644
--- a/.php_cs
+++ b/.php_cs
@@ -1,5 +1,7 @@
 <?php
 
+require_once __DIR__.'/vendor/sllh/php-cs-fixer-styleci-bridge/autoload.php';
+
 $header = <<<EOF
 This file is part of the RollerworksDatagrid package.
 
@@ -9,25 +11,16 @@ This source file is subject to the MIT license that is bundled
 with this source code in the file LICENSE.
 EOF;
 
-Symfony\CS\Fixer\Contrib\HeaderCommentFixer::setHeader($header);
+$config = SLLH\StyleCIBridge\ConfigBridge::create()
+    ->setUsingCache(true)
+    ->setRiskyAllowed(true)
+;
 
-return Symfony\CS\Config\Config::create()
-    ->setUsingLinter(false)
-    // use SYMFONY_LEVEL:
-    ->level(Symfony\CS\FixerInterface::SYMFONY_LEVEL)
-    // and extra fixers:
-    ->fixers(array(
-        'ordered_use',
-        //'strict',
-        'strict_param',
-        'short_array_syntax',
-        'phpdoc_order',
-        'header_comment',
-        '-psr0',
-    ))
-    ->finder(
-        Symfony\CS\Finder\DefaultFinder::create()
-            ->exclude(array('bin', 'doc'))
-            ->in(__DIR__)
+$config->setRules(
+    array_merge(
+        $config->getRules(),
+        ['header_comment' => ['header' => $header]]
     )
-;
+);
+
+return $config;
diff --git a/.styleci.yml b/.styleci.yml
new file mode 100644
index 0000000..08cbe17
--- /dev/null
+++ b/.styleci.yml
@@ -0,0 +1,20 @@
+preset: symfony
+
+risky: true
+
+linting: false
+
+enabled:
+    #- ordered_class_elements
+    - ordered_imports
+    - phpdoc_order
+    - short_array_syntax
+    - strict_param
+    #- declare_strict_types
+
+finder:
+    path:
+        - 'src/'
+        - 'tests/'
+    not-path:
+        - 'Fixtures'
diff --git a/composer.json b/composer.json
index bd7ef68..2c2a308 100644
--- a/composer.json
+++ b/composer.json
@@ -21,7 +21,8 @@
         "symfony/intl": "^3.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.5"
+        "phpunit/phpunit": "^5.5",
+        "sllh/php-cs-fixer-styleci-bridge": "^2.1"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/AbstractDatagridExtension.php b/src/AbstractDatagridExtension.php
index bb88e40..22cdce4 100644
--- a/src/AbstractDatagridExtension.php
+++ b/src/AbstractDatagridExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -38,7 +38,7 @@ abstract class AbstractDatagridExtension implements DatagridExtensionInterface
     /**
      * {@inheritdoc}
      */
-    public function getType($type)
+    public function getType($type): ColumnTypeInterface
     {
         if (null === $this->types) {
             $this->initColumnTypes();
@@ -54,7 +54,7 @@ public function getType($type)
     /**
      * {@inheritdoc}
      */
-    public function hasType($type)
+    public function hasType($type): bool
     {
         if (null === $this->types) {
             $this->initColumnTypes();
@@ -66,7 +66,7 @@ public function hasType($type)
     /**
      * {@inheritdoc}
      */
-    public function hasTypeExtensions($type)
+    public function hasTypeExtensions($type): bool
     {
         if (null === $this->typesExtensions) {
             $this->initTypesExtensions();
@@ -78,7 +78,7 @@ public function hasTypeExtensions($type)
     /**
      * {@inheritdoc}
      */
-    public function getTypeExtensions($type)
+    public function getTypeExtensions($type): array
     {
         if (null === $this->typesExtensions) {
             $this->initTypesExtensions();
@@ -96,7 +96,7 @@ public function getTypeExtensions($type)
      *
      * @codeCoverageIgnore
      */
-    protected function loadTypes()
+    protected function loadTypes(): array
     {
         return [];
     }
@@ -110,7 +110,7 @@ protected function loadTypes()
      *
      * @codeCoverageIgnore
      */
-    protected function loadTypesExtensions()
+    protected function loadTypesExtensions(): array
     {
         return [];
     }
diff --git a/src/Column/AbstractType.php b/src/Column/AbstractType.php
index 5c73886..11f6e6b 100644
--- a/src/Column/AbstractType.php
+++ b/src/Column/AbstractType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -56,7 +56,7 @@ public function buildHeaderView(HeaderView $view, ColumnInterface $column, array
      *
      * @return string The prefix of the template block name
      */
-    public function getBlockPrefix()
+    public function getBlockPrefix(): string
     {
         return StringUtil::fqcnToBlockPrefix(get_class($this));
     }
diff --git a/src/Column/AbstractTypeExtension.php b/src/Column/AbstractTypeExtension.php
index c46884f..5d91bf1 100644
--- a/src/Column/AbstractTypeExtension.php
+++ b/src/Column/AbstractTypeExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Column/CellView.php b/src/Column/CellView.php
index 596eda0..ee6cb91 100644
--- a/src/Column/CellView.php
+++ b/src/Column/CellView.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Column/Column.php b/src/Column/Column.php
index d42389c..06533e8 100644
--- a/src/Column/Column.php
+++ b/src/Column/Column.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -83,7 +83,7 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function getName()
+    public function getName(): string
     {
         return $this->name;
     }
@@ -91,7 +91,7 @@ public function getName()
     /**
      * {@inheritdoc}
      */
-    public function getType()
+    public function getType(): ResolvedColumnTypeInterface
     {
         return $this->type;
     }
@@ -131,7 +131,7 @@ public function resetViewTransformers()
     /**
      * {@inheritdoc}
      */
-    public function getViewTransformers()
+    public function getViewTransformers(): array
     {
         return $this->viewTransformers;
     }
@@ -139,7 +139,7 @@ public function getViewTransformers()
     /**
      * {@inheritdoc}
      */
-    public function getOptions()
+    public function getOptions(): array
     {
         return $this->options;
     }
@@ -159,7 +159,7 @@ public function getOption($name, $default = null)
     /**
      * {@inheritdoc}
      */
-    public function hasOption($name)
+    public function hasOption($name): bool
     {
         return array_key_exists($name, $this->options);
     }
@@ -167,7 +167,7 @@ public function hasOption($name)
     /**
      * {@inheritdoc}
      */
-    public function createHeaderView(DatagridView $datagrid)
+    public function createHeaderView(DatagridView $datagrid): HeaderView
     {
         // The methods createHeaderView(), buildHeaderView() are called
         // explicitly here in order to be able to override either of them
@@ -182,7 +182,7 @@ public function createHeaderView(DatagridView $datagrid)
     /**
      * {@inheritdoc}
      */
-    public function createCellView(DatagridView $datagrid, $object, $index)
+    public function createCellView(DatagridView $datagrid, $object, $index): CellView
     {
         // The methods createCellView(), buildCellView() are called
         // explicitly here in order to be able to override either of them
@@ -214,7 +214,7 @@ public function setDataProvider(callable $dataProvider)
      *
      * @return callable
      */
-    public function getDataProvider()
+    public function getDataProvider(): callable
     {
         return $this->dataProvider;
     }
diff --git a/src/Column/ColumnInterface.php b/src/Column/ColumnInterface.php
index 0e0db4c..9fe2b6b 100644
--- a/src/Column/ColumnInterface.php
+++ b/src/Column/ColumnInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -24,14 +24,14 @@ interface ColumnInterface
      *
      * @return string
      */
-    public function getName();
+    public function getName(): string;
 
     /**
      * Returns the column-type name.
      *
      * @return ResolvedColumnTypeInterface
      */
-    public function getType();
+    public function getType(): ResolvedColumnTypeInterface;
 
     /**
      * Appends / prepends a transformer to the view transformer chain.
@@ -58,14 +58,14 @@ public function resetViewTransformers();
      *
      * @return DataTransformerInterface[] An array of {@link DataTransformerInterface} instances
      */
-    public function getViewTransformers();
+    public function getViewTransformers(): array;
 
     /**
      * Returns all options passed during the construction of the column.
      *
      * @return array The passed options
      */
-    public function getOptions();
+    public function getOptions(): array;
 
     /**
      * Returns the value of a specific option.
@@ -84,14 +84,14 @@ public function getOption($name, $default = null);
      *
      * @return bool
      */
-    public function hasOption($name);
+    public function hasOption($name): bool;
 
     /**
      * @param DatagridView $datagrid
      *
      * @return HeaderView
      */
-    public function createHeaderView(DatagridView $datagrid);
+    public function createHeaderView(DatagridView $datagrid): HeaderView;
 
     /**
      * @param DatagridView $datagrid
@@ -100,7 +100,7 @@ public function createHeaderView(DatagridView $datagrid);
      *
      * @return CellView
      */
-    public function createCellView(DatagridView $datagrid, $object, $index);
+    public function createCellView(DatagridView $datagrid, $object, $index): CellView;
 
     /**
      * Set the data-provider for the column.
@@ -114,5 +114,5 @@ public function setDataProvider(callable $dataProvider);
      *
      * @return callable
      */
-    public function getDataProvider();
+    public function getDataProvider(): callable;
 }
diff --git a/src/Column/ColumnTypeExtensionInterface.php b/src/Column/ColumnTypeExtensionInterface.php
index d437283..3216603 100644
--- a/src/Column/ColumnTypeExtensionInterface.php
+++ b/src/Column/ColumnTypeExtensionInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -50,5 +50,5 @@ public function configureOptions(OptionsResolver $optionsResolver);
      *
      * @return string The name of the type being extended
      */
-    public function getExtendedType();
+    public function getExtendedType(): string;
 }
diff --git a/src/Column/ColumnTypeInterface.php b/src/Column/ColumnTypeInterface.php
index b61135d..f43efb4 100644
--- a/src/Column/ColumnTypeInterface.php
+++ b/src/Column/ColumnTypeInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -56,7 +56,7 @@ public function buildHeaderView(HeaderView $view, ColumnInterface $column, array
      *
      * @return string The prefix of the template block name
      */
-    public function getBlockPrefix();
+    public function getBlockPrefix(): string;
 
     /**
      * Returns the fully-qualified class name of the parent type.
diff --git a/src/Column/ColumnTypeRegistry.php b/src/Column/ColumnTypeRegistry.php
index 8d1c425..6da6797 100644
--- a/src/Column/ColumnTypeRegistry.php
+++ b/src/Column/ColumnTypeRegistry.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -50,7 +50,7 @@ public function __construct(array $extensions, ResolvedColumnTypeFactoryInterfac
     {
         foreach ($extensions as $extension) {
             if (!$extension instanceof DatagridExtensionInterface) {
-                throw new UnexpectedTypeException($extension, 'Rollerworks\Component\Datagrid\DatagridExtensionInterface');
+                throw new UnexpectedTypeException($extension, DatagridExtensionInterface::class);
             }
         }
 
@@ -61,7 +61,7 @@ public function __construct(array $extensions, ResolvedColumnTypeFactoryInterfac
     /**
      * {@inheritdoc}
      */
-    public function getType($name)
+    public function getType($name): ResolvedColumnTypeInterface
     {
         if (!isset($this->types[$name])) {
             $type = null;
@@ -92,7 +92,7 @@ public function getType($name)
     /**
      * {@inheritdoc}
      */
-    public function hasType($name)
+    public function hasType($name): bool
     {
         if (isset($this->types[$name])) {
             return true;
@@ -110,20 +110,12 @@ public function hasType($name)
     /**
      * {@inheritdoc}
      */
-    public function getExtensions()
+    public function getExtensions(): array
     {
         return $this->extensions;
     }
 
-    /**
-     * Wraps a type into a ResolvedFormTypeInterface implementation and connects
-     * it with its parent type.
-     *
-     * @param ColumnTypeInterface $type The type to resolve
-     *
-     * @return ResolvedColumnTypeInterface The resolved type
-     */
-    private function resolveType(ColumnTypeInterface $type)
+    private function resolveType(ColumnTypeInterface $type): ResolvedColumnTypeInterface
     {
         $parentType = $type->getParent();
         $fqcn = get_class($type);
diff --git a/src/Column/ColumnTypeRegistryInterface.php b/src/Column/ColumnTypeRegistryInterface.php
index 35fd322..a887c50 100644
--- a/src/Column/ColumnTypeRegistryInterface.php
+++ b/src/Column/ColumnTypeRegistryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -32,7 +32,7 @@ interface ColumnTypeRegistryInterface
      *
      * @return ResolvedColumnTypeInterface The type
      */
-    public function getType($name);
+    public function getType($name): ResolvedColumnTypeInterface;
 
     /**
      * Returns whether the given column type is supported.
@@ -41,12 +41,12 @@ public function getType($name);
      *
      * @return bool Whether the type is supported
      */
-    public function hasType($name);
+    public function hasType($name): bool;
 
     /**
      * Returns the extensions loaded by the component.
      *
      * @return DatagridExtensionInterface[]
      */
-    public function getExtensions();
+    public function getExtensions(): array;
 }
diff --git a/src/Column/HeaderView.php b/src/Column/HeaderView.php
index 0c02e5a..c7c1563 100644
--- a/src/Column/HeaderView.php
+++ b/src/Column/HeaderView.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Column/ResolvedColumnType.php b/src/Column/ResolvedColumnType.php
index 888d3f7..7b2d353 100644
--- a/src/Column/ResolvedColumnType.php
+++ b/src/Column/ResolvedColumnType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -67,7 +67,7 @@ public function __construct(ColumnTypeInterface $innerType, array $typeExtension
     /**
      * {@inheritdoc}
      */
-    public function getBlockPrefix()
+    public function getBlockPrefix(): string
     {
         return $this->innerType->getBlockPrefix();
     }
@@ -87,7 +87,7 @@ public function getParent()
      *
      * @return ColumnTypeInterface The wrapped column type
      */
-    public function getInnerType()
+    public function getInnerType(): ColumnTypeInterface
     {
         return $this->innerType;
     }
@@ -97,7 +97,7 @@ public function getInnerType()
      *
      * @return ColumnTypeExtensionInterface[] An array of {@link ColumnTypeExtensionInterface} instances
      */
-    public function getTypeExtensions()
+    public function getTypeExtensions(): array
     {
         return $this->typeExtensions;
     }
@@ -132,7 +132,7 @@ public function buildType(ColumnInterface $config, array $options)
      *
      * @return ColumnInterface
      */
-    public function createColumn($name, array $options = [])
+    public function createColumn(string $name, array $options = []): ColumnInterface
     {
         $options = $this->getOptionsResolver()->resolve($options);
         $builder = $this->newColumn($name, $options);
@@ -143,7 +143,7 @@ public function createColumn($name, array $options = [])
     /**
      * {inheritdoc}.
      */
-    public function createHeaderView(ColumnInterface $column, DatagridView $datagrid)
+    public function createHeaderView(ColumnInterface $column, DatagridView $datagrid): HeaderView
     {
         $view = new HeaderView($column, $datagrid, $column->getOption('label'));
 
@@ -153,7 +153,7 @@ public function createHeaderView(ColumnInterface $column, DatagridView $datagrid
     /**
      * {inheritdoc}.
      */
-    public function createCellView(ColumnInterface $column, DatagridView $datagrid)
+    public function createCellView(ColumnInterface $column, DatagridView $datagrid): CellView
     {
         $view = new CellView($column, $datagrid);
 
@@ -220,7 +220,7 @@ public function getValue(ColumnInterface $column, $object, $useTransformers = tr
      *
      * @return OptionsResolver The options resolver
      */
-    public function getOptionsResolver()
+    public function getOptionsResolver(): OptionsResolver
     {
         if (null === $this->optionsResolver) {
             if (null !== $this->parent) {
@@ -247,9 +247,9 @@ public function getOptionsResolver()
      * @param string $name    The name of the column
      * @param array  $options The builder options
      *
-     * @return Column The new field instance
+     * @return ColumnInterface The new field instance
      */
-    protected function newColumn($name, array $options)
+    protected function newColumn($name, array $options): ColumnInterface
     {
         return new Column($name, $this, $options);
     }
diff --git a/src/Column/ResolvedColumnTypeFactory.php b/src/Column/ResolvedColumnTypeFactory.php
index 01e03ac..dfc3f25 100644
--- a/src/Column/ResolvedColumnTypeFactory.php
+++ b/src/Column/ResolvedColumnTypeFactory.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -16,7 +16,7 @@ class ResolvedColumnTypeFactory implements ResolvedColumnTypeFactoryInterface
     /**
      * {@inheritdoc}
      */
-    public function createResolvedType(ColumnTypeInterface $type, array $typeExtensions, ResolvedColumnTypeInterface $parent = null)
+    public function createResolvedType(ColumnTypeInterface $type, array $typeExtensions, ResolvedColumnTypeInterface $parent = null): ResolvedColumnTypeInterface
     {
         return new ResolvedColumnType($type, $typeExtensions, $parent);
     }
diff --git a/src/Column/ResolvedColumnTypeFactoryInterface.php b/src/Column/ResolvedColumnTypeFactoryInterface.php
index e8f9ddb..d774596 100644
--- a/src/Column/ResolvedColumnTypeFactoryInterface.php
+++ b/src/Column/ResolvedColumnTypeFactoryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -31,5 +31,5 @@ interface ResolvedColumnTypeFactoryInterface
      *
      * @return ResolvedColumnTypeInterface
      */
-    public function createResolvedType(ColumnTypeInterface $type, array $typeExtensions, ResolvedColumnTypeInterface $parent = null);
+    public function createResolvedType(ColumnTypeInterface $type, array $typeExtensions, ResolvedColumnTypeInterface $parent = null): ResolvedColumnTypeInterface;
 }
diff --git a/src/Column/ResolvedColumnTypeInterface.php b/src/Column/ResolvedColumnTypeInterface.php
index 0a7a297..0fdaaac 100644
--- a/src/Column/ResolvedColumnTypeInterface.php
+++ b/src/Column/ResolvedColumnTypeInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -12,6 +12,7 @@
 namespace Rollerworks\Component\Datagrid\Column;
 
 use Rollerworks\Component\Datagrid\DatagridView;
+use Symfony\Component\OptionsResolver\OptionsResolver;
 
 /**
  * A wrapper for a field type and its extensions.
@@ -25,7 +26,7 @@ interface ResolvedColumnTypeInterface
      *
      * @return string The prefix of the template block name
      */
-    public function getBlockPrefix();
+    public function getBlockPrefix(): string;
 
     /**
      * Returns the parent type.
@@ -39,14 +40,14 @@ public function getParent();
      *
      * @return ColumnTypeInterface The wrapped form type
      */
-    public function getInnerType();
+    public function getInnerType(): ColumnTypeInterface;
 
     /**
      * Returns the extensions of the wrapped column type.
      *
      * @return ColumnTypeExtensionInterface[] An array of {@link ColumnTypeExtensionInterface} instances
      */
-    public function getTypeExtensions();
+    public function getTypeExtensions(): array;
 
     /**
      * Returns a new ColumnInterface instance.
@@ -56,7 +57,7 @@ public function getTypeExtensions();
      *
      * @return ColumnInterface
      */
-    public function createColumn($name, array $options = []);
+    public function createColumn(string $name, array $options = []): ColumnInterface;
 
     /**
      * This configures the {@link ColumnInterface} instance.
@@ -77,7 +78,7 @@ public function buildType(ColumnInterface $config, array $options);
      *
      * @return HeaderView
      */
-    public function createHeaderView(ColumnInterface $column, DatagridView $datagrid);
+    public function createHeaderView(ColumnInterface $column, DatagridView $datagrid): HeaderView;
 
     /**
      * Creates a new cell view for a column of this type.
@@ -87,7 +88,7 @@ public function createHeaderView(ColumnInterface $column, DatagridView $datagrid
      *
      * @return CellView
      */
-    public function createCellView(ColumnInterface $column, DatagridView $datagrid);
+    public function createCellView(ColumnInterface $column, DatagridView $datagrid): CellView;
 
     /**
      * Configures a header view for the type hierarchy.
@@ -110,12 +111,12 @@ public function buildCellView(CellView $view, ColumnInterface $column, array $op
     /**
      * Returns the configured options resolver used for this type.
      *
-     * @return \Symfony\Component\OptionsResolver\OptionsResolver The options resolver
+     * @return OptionsResolver The options resolver
      */
-    public function getOptionsResolver();
+    public function getOptionsResolver(): OptionsResolver;
 
     /**
-     * Get of the column.
+     * Get the value of the column.
      *
      * @param ColumnInterface $column
      * @param mixed           $object
diff --git a/src/DataTransformerInterface.php b/src/DataTransformerInterface.php
index f726ddf..a3a8868 100644
--- a/src/DataTransformerInterface.php
+++ b/src/DataTransformerInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Datagrid.php b/src/Datagrid.php
index d1bc15d..ab260ac 100644
--- a/src/Datagrid.php
+++ b/src/Datagrid.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -82,7 +82,7 @@ public function __construct($name, array $columns, callable $viewBuilder = null)
     /**
      * {@inheritdoc}
      */
-    public function getName()
+    public function getName(): string
     {
         return $this->name;
     }
@@ -90,7 +90,7 @@ public function getName()
     /**
      * {@inheritdoc}
      */
-    public function getColumn($name)
+    public function getColumn($name): ColumnInterface
     {
         if (!isset($this->columns[$name])) {
             throw new UnknownColumnException($name, $this);
@@ -102,7 +102,7 @@ public function getColumn($name)
     /**
      * {@inheritdoc}
      */
-    public function getColumns()
+    public function getColumns(): array
     {
         return $this->columns;
     }
@@ -110,7 +110,7 @@ public function getColumns()
     /**
      * {@inheritdoc}
      */
-    public function hasColumn($name)
+    public function hasColumn($name): bool
     {
         return isset($this->columns[$name]);
     }
@@ -118,7 +118,7 @@ public function hasColumn($name)
     /**
      * {@inheritdoc}
      */
-    public function hasColumnType($type)
+    public function hasColumnType($type): bool
     {
         foreach ($this->columns as $column) {
             if ($column->getType()->getInnerType() instanceof $type) {
@@ -158,7 +158,7 @@ public function getData()
     /**
      * {@inheritdoc}
      */
-    public function createView()
+    public function createView(): DatagridView
     {
         if (!isset($this->data)) {
             throw new BadMethodCallException(
diff --git a/src/DatagridBuilder.php b/src/DatagridBuilder.php
index 65e6056..c2d992e 100644
--- a/src/DatagridBuilder.php
+++ b/src/DatagridBuilder.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/DatagridBuilderInterface.php b/src/DatagridBuilderInterface.php
index c9cc32e..874c8e6 100644
--- a/src/DatagridBuilderInterface.php
+++ b/src/DatagridBuilderInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/DatagridExtensionInterface.php b/src/DatagridExtensionInterface.php
index 1087f15..9ef2bf5 100644
--- a/src/DatagridExtensionInterface.php
+++ b/src/DatagridExtensionInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -27,7 +27,7 @@ interface DatagridExtensionInterface
      *
      * @return bool
      */
-    public function hasType($type);
+    public function hasType($type): bool;
 
     /**
      * Get column type.
@@ -38,7 +38,7 @@ public function hasType($type);
      *
      * @return ColumnTypeInterface
      */
-    public function getType($type);
+    public function getType($type): ColumnTypeInterface;
 
     /**
      * Check if extension has any column type extension for column of $type.
@@ -47,7 +47,7 @@ public function getType($type);
      *
      * @return bool
      */
-    public function hasTypeExtensions($type);
+    public function hasTypeExtensions($type): bool;
 
     /**
      * Return extensions for column type provided by this data grid extension.
@@ -56,5 +56,5 @@ public function hasTypeExtensions($type);
      *
      * @return ColumnTypeExtensionInterface[]
      */
-    public function getTypeExtensions($type);
+    public function getTypeExtensions($type): array;
 }
diff --git a/src/DatagridFactory.php b/src/DatagridFactory.php
index 7e5ea94..2b2cd5d 100644
--- a/src/DatagridFactory.php
+++ b/src/DatagridFactory.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -11,8 +11,8 @@
 
 namespace Rollerworks\Component\Datagrid;
 
+use Rollerworks\Component\Datagrid\Column\ColumnInterface;
 use Rollerworks\Component\Datagrid\Column\ColumnTypeRegistryInterface;
-use Rollerworks\Component\Datagrid\Exception\UnexpectedTypeException;
 
 /**
  * @author Sebastiaan Stok <s.stok@rollerscapes.net>
@@ -35,7 +35,7 @@ public function __construct(ColumnTypeRegistryInterface $registry)
     /**
      * {@inheritdoc}
      */
-    public function createDatagrid($name, array $columns)
+    public function createDatagrid(string $name, array $columns): DatagridInterface
     {
         return new Datagrid($name, $columns);
     }
@@ -43,7 +43,7 @@ public function createDatagrid($name, array $columns)
     /**
      * {@inheritdoc}
      */
-    public function createDatagridBuilder($name)
+    public function createDatagridBuilder(string $name): DatagridBuilderInterface
     {
         return new DatagridBuilder($this, $name);
     }
@@ -51,18 +51,14 @@ public function createDatagridBuilder($name)
     /**
      * {@inheritdoc}
      */
-    public function createColumn($name, $type, array $options = [])
+    public function createColumn(string $name, string $type, array $options = []): ColumnInterface
     {
-        if (!is_string($type)) {
-            throw new UnexpectedTypeException($type, 'string');
-        }
-
         $type = $this->typeRegistry->getType($type);
 
         $column = $type->createColumn($name, $options);
 
         // Explicitly call buildType() in order to be able to override either
-        // createColumn() or buildType() in the resolved column type
+        // createColumn() or buildType() in the resolved column type.
         $type->buildType($column, $column->getOptions());
 
         return $column;
diff --git a/src/DatagridFactoryInterface.php b/src/DatagridFactoryInterface.php
index 2f459da..29a2586 100644
--- a/src/DatagridFactoryInterface.php
+++ b/src/DatagridFactoryInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -27,7 +27,7 @@ interface DatagridFactoryInterface
      *
      * @return ColumnInterface
      */
-    public function createColumn($name, $type, array $options = []);
+    public function createColumn(string $name, string $type, array $options = []): ColumnInterface;
 
     /**
      * Create a new DatagridInterface instance with a unique name.
@@ -37,7 +37,7 @@ public function createColumn($name, $type, array $options = []);
      *
      * @return DatagridInterface
      */
-    public function createDatagrid($name, array $columns);
+    public function createDatagrid(string $name, array $columns): DatagridInterface;
 
     /**
      * Create a new DatagridBuilderInterface instance.
@@ -46,5 +46,5 @@ public function createDatagrid($name, array $columns);
      *
      * @return DatagridBuilderInterface
      */
-    public function createDatagridBuilder($name);
+    public function createDatagridBuilder(string $name): DatagridBuilderInterface;
 }
diff --git a/src/DatagridInterface.php b/src/DatagridInterface.php
index 4c904c7..42f6968 100644
--- a/src/DatagridInterface.php
+++ b/src/DatagridInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -26,7 +26,7 @@ interface DatagridInterface
      *
      * @return string
      */
-    public function getName();
+    public function getName(): string;
 
     /**
      * Return column with by name.
@@ -37,14 +37,14 @@ public function getName();
      *
      * @return ColumnInterface
      */
-    public function getColumn($name);
+    public function getColumn($name): ColumnInterface;
 
     /**
      * Return all registered columns in the datagrid.
      *
      * @return ColumnInterface[]
      */
-    public function getColumns();
+    public function getColumns(): array;
 
     /**
      * Get if the column is registered on the datagrid.
@@ -53,7 +53,7 @@ public function getColumns();
      *
      * @return bool
      */
-    public function hasColumn($name);
+    public function hasColumn($name): bool;
 
     /**
      * Get whether column with a specific type is registered
@@ -63,7 +63,7 @@ public function hasColumn($name);
      *
      * @return bool
      */
-    public function hasColumnType($type);
+    public function hasColumnType($type): bool;
 
     /**
      * Create a new DatagridView object for rendering the datagrid.
@@ -73,7 +73,7 @@ public function hasColumnType($type);
      *
      * @return DatagridView
      */
-    public function createView();
+    public function createView(): DatagridView;
 
     /**
      * Set the data collection of the datagrid.
diff --git a/src/DatagridRowView.php b/src/DatagridRowView.php
index 7d442f3..878d9cc 100644
--- a/src/DatagridRowView.php
+++ b/src/DatagridRowView.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -55,7 +55,7 @@ class DatagridRowView implements \IteratorAggregate, \Countable
      * @param mixed             $source
      * @param int               $index
      */
-    public function __construct(DatagridView $datagridView, array $columns, $source, $index)
+    public function __construct(DatagridView $datagridView, array $columns, $source, int $index)
     {
         $this->datagrid = $datagridView;
         $this->source = $source;
diff --git a/src/DatagridView.php b/src/DatagridView.php
index cf6f498..7e48b48 100644
--- a/src/DatagridView.php
+++ b/src/DatagridView.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -54,11 +54,6 @@ class DatagridView implements \IteratorAggregate, \Countable
      */
     public $vars = [];
 
-    /**
-     * Constructor.
-     *
-     * @param DatagridInterface $datagrid
-     */
     public function __construct(DatagridInterface $datagrid)
     {
         $this->name = $datagrid->getName();
@@ -77,18 +72,12 @@ public function __construct(DatagridInterface $datagrid)
         }
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function hasColumn($name)
+    public function hasColumn(string $name): bool
     {
         return isset($this->columns[$name]);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getColumn($name)
+    public function getColumn(string $name): HeaderView
     {
         if (isset($this->columns[$name])) {
             return $this->columns[$name];
@@ -108,7 +97,7 @@ public function getColumn($name)
      *
      * @return mixed
      */
-    public function getVar($key, $default = null)
+    public function getVar(string $key, $default = null)
     {
         if (array_key_exists($key, $this->vars)) {
             return $this->vars[$key];
diff --git a/src/Exception/BadMethodCallException.php b/src/Exception/BadMethodCallException.php
index d8299f8..dbc88c7 100644
--- a/src/Exception/BadMethodCallException.php
+++ b/src/Exception/BadMethodCallException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/DataMappingException.php b/src/Exception/DataMappingException.php
index 5c9a06c..56e2ba0 100644
--- a/src/Exception/DataMappingException.php
+++ b/src/Exception/DataMappingException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/DataProviderException.php b/src/Exception/DataProviderException.php
index 206532c..659fd24 100644
--- a/src/Exception/DataProviderException.php
+++ b/src/Exception/DataProviderException.php
@@ -1,10 +1,19 @@
-<?php
+<?php declare(strict_types=1);
+
+/*
+ * This file is part of the RollerworksDatagrid package.
+ *
+ * (c) Sebastiaan Stok <s.stok@rollerscapes.net>
+ *
+ * This source file is subject to the MIT license that is bundled
+ * with this source code in the file LICENSE.
+ */
 
 namespace Rollerworks\Component\Datagrid\Exception;
 
 final class DataProviderException extends \RuntimeException implements ExceptionInterface
 {
-    public static function autoAccessorUnableToGetValue($columnName, \Exception $previous = null)
+    public static function autoAccessorUnableToGetValue(string $columnName, \Exception $previous = null)
     {
         return new self(
             sprintf('Unable to get value for column "%s". Consider setting the "data_provider" option.', $columnName),
diff --git a/src/Exception/DatagridColumnException.php b/src/Exception/DatagridColumnException.php
index 1bf6156..da60453 100644
--- a/src/Exception/DatagridColumnException.php
+++ b/src/Exception/DatagridColumnException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/DatagridException.php b/src/Exception/DatagridException.php
index cdca8d3..ab491eb 100644
--- a/src/Exception/DatagridException.php
+++ b/src/Exception/DatagridException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/ExceptionInterface.php b/src/Exception/ExceptionInterface.php
index 15c6b69..cae324a 100644
--- a/src/Exception/ExceptionInterface.php
+++ b/src/Exception/ExceptionInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/InvalidArgumentException.php b/src/Exception/InvalidArgumentException.php
index d6dd0a6..1d70d2c 100644
--- a/src/Exception/InvalidArgumentException.php
+++ b/src/Exception/InvalidArgumentException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/InvalidConfigurationException.php b/src/Exception/InvalidConfigurationException.php
index cac59cc..25f5280 100644
--- a/src/Exception/InvalidConfigurationException.php
+++ b/src/Exception/InvalidConfigurationException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/TransformationFailedException.php b/src/Exception/TransformationFailedException.php
index d01f16d..044885f 100644
--- a/src/Exception/TransformationFailedException.php
+++ b/src/Exception/TransformationFailedException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Exception/UnexpectedTypeException.php b/src/Exception/UnexpectedTypeException.php
index a5a963d..68ad57d 100644
--- a/src/Exception/UnexpectedTypeException.php
+++ b/src/Exception/UnexpectedTypeException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -14,7 +14,7 @@
 class UnexpectedTypeException extends DatagridException
 {
     /**
-     * @param string       $value
+     * @param mixed        $value
      * @param string|array $expectedType
      */
     public function __construct($value, $expectedType)
diff --git a/src/Exception/UnknownColumnException.php b/src/Exception/UnknownColumnException.php
index cb21680..3d2840c 100644
--- a/src/Exception/UnknownColumnException.php
+++ b/src/Exception/UnknownColumnException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -45,7 +45,7 @@ public function __construct($columnName, DatagridInterface $datagrid)
     /**
      * @return DatagridInterface
      */
-    public function getDatagrid()
+    public function getDatagrid(): DatagridInterface
     {
         return $this->datagrid;
     }
@@ -53,7 +53,7 @@ public function getDatagrid()
     /**
      * @return string
      */
-    public function getColumnName()
+    public function getColumnName(): string
     {
         return $this->columnName;
     }
diff --git a/src/Extension/Core/CoreExtension.php b/src/Extension/Core/CoreExtension.php
index e8b9f8b..c7fe4e6 100644
--- a/src/Extension/Core/CoreExtension.php
+++ b/src/Extension/Core/CoreExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -22,7 +22,7 @@ class CoreExtension extends AbstractDatagridExtension
     /**
      * {@inheritdoc}
      */
-    protected function loadTypes()
+    protected function loadTypes(): array
     {
         $propertyAccessor = PropertyAccess::createPropertyAccessor();
 
@@ -43,7 +43,7 @@ protected function loadTypes()
     /**
      * {@inheritdoc}
      */
-    protected function loadTypesExtensions()
+    protected function loadTypesExtensions(): array
     {
         return [
             new TypeExtension\ColumnOrderExtension(),
diff --git a/src/Extension/Core/DataTransformer/ArrayToDateTimeTransformer.php b/src/Extension/Core/DataTransformer/ArrayToDateTimeTransformer.php
index df32fd7..6c04484 100644
--- a/src/Extension/Core/DataTransformer/ArrayToDateTimeTransformer.php
+++ b/src/Extension/Core/DataTransformer/ArrayToDateTimeTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/BaseDateTimeTransformer.php b/src/Extension/Core/DataTransformer/BaseDateTimeTransformer.php
index 1d6f16d..55eafbb 100644
--- a/src/Extension/Core/DataTransformer/BaseDateTimeTransformer.php
+++ b/src/Extension/Core/DataTransformer/BaseDateTimeTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/CompoundColumnTransformer.php b/src/Extension/Core/DataTransformer/CompoundColumnTransformer.php
index 534e6fa..7516024 100644
--- a/src/Extension/Core/DataTransformer/CompoundColumnTransformer.php
+++ b/src/Extension/Core/DataTransformer/CompoundColumnTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformer.php b/src/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformer.php
index eafae86..c2a5294 100644
--- a/src/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformer.php
+++ b/src/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -114,7 +114,7 @@ protected function getIntlDateFormatter()
         $timeFormat = $this->timeFormat;
         $timezone = $this->outputTimezone;
         $calendar = $this->calendar;
-        $pattern = $this->pattern;
+        $pattern = $this->pattern ?? '';
 
         $intlDateFormatter = new \IntlDateFormatter(\Locale::getDefault(), $dateFormat, $timeFormat, $timezone, $calendar, $pattern);
         $intlDateFormatter->setLenient(false);
diff --git a/src/Extension/Core/DataTransformer/EmptyValueTransformer.php b/src/Extension/Core/DataTransformer/EmptyValueTransformer.php
index 55b4d2f..5085a21 100644
--- a/src/Extension/Core/DataTransformer/EmptyValueTransformer.php
+++ b/src/Extension/Core/DataTransformer/EmptyValueTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php b/src/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php
index 2a94796..66541b5 100644
--- a/src/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php
+++ b/src/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/MoneyToLocalizedStringTransformer.php b/src/Extension/Core/DataTransformer/MoneyToLocalizedStringTransformer.php
index a294a3d..dd21d10 100644
--- a/src/Extension/Core/DataTransformer/MoneyToLocalizedStringTransformer.php
+++ b/src/Extension/Core/DataTransformer/MoneyToLocalizedStringTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php b/src/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php
index b3ea91e..db326e8 100644
--- a/src/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php
+++ b/src/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/DataTransformer/StringToDateTimeTransformer.php b/src/Extension/Core/DataTransformer/StringToDateTimeTransformer.php
index 246079e..c53ca0b 100644
--- a/src/Extension/Core/DataTransformer/StringToDateTimeTransformer.php
+++ b/src/Extension/Core/DataTransformer/StringToDateTimeTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -60,12 +60,12 @@ public function __construct($inputTimezone = null, $outputTimezone = null, $form
      *                                       if the date could not be parsed or
      *                                       if the input timezone is not supported
      *
-     * @return \DateTime An instance of \DateTime
+     * @return \DateTime|null An instance of \DateTime
      */
     public function transform($value)
     {
         if (empty($value)) {
-            return;
+            return null;
         }
 
         if (!is_string($value)) {
@@ -88,7 +88,7 @@ public function transform($value)
             }
 
             if ($this->inputTimezone !== $this->outputTimezone) {
-                $dateTime->setTimeZone(new \DateTimeZone($this->inputTimezone));
+                $dateTime->setTimezone(new \DateTimeZone($this->inputTimezone));
             }
         } catch (TransformationFailedException $e) {
             throw $e;
diff --git a/src/Extension/Core/DataTransformer/TimestampToDateTimeTransformer.php b/src/Extension/Core/DataTransformer/TimestampToDateTimeTransformer.php
index 8bc6499..76681bd 100644
--- a/src/Extension/Core/DataTransformer/TimestampToDateTimeTransformer.php
+++ b/src/Extension/Core/DataTransformer/TimestampToDateTimeTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -29,12 +29,12 @@ class TimestampToDateTimeTransformer extends BaseDateTimeTransformer
      * @throws TransformationFailedException If the given value is not a timestamp
      *                                       or if the given timestamp is invalid
      *
-     * @return \DateTime A \DateTime object
+     * @return \DateTime|null
      */
     public function transform($value)
     {
         if (null === $value) {
-            return;
+            return null;
         }
 
         if (!is_numeric($value)) {
@@ -44,7 +44,7 @@ public function transform($value)
         try {
             $dateTime = new \DateTime();
             $dateTime->setTimezone(new \DateTimeZone($this->outputTimezone));
-            $dateTime->setTimestamp($value);
+            $dateTime->setTimestamp((int) $value);
 
             if ($this->inputTimezone !== $this->outputTimezone) {
                 $dateTime->setTimezone(new \DateTimeZone($this->inputTimezone));
diff --git a/src/Extension/Core/DataTransformer/ValueFormatTransformer.php b/src/Extension/Core/DataTransformer/ValueFormatTransformer.php
index b9b318a..e0992d2 100644
--- a/src/Extension/Core/DataTransformer/ValueFormatTransformer.php
+++ b/src/Extension/Core/DataTransformer/ValueFormatTransformer.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -72,7 +72,7 @@ public function transform($value)
         return $this->formatValue($value, $this->format, $this->glue);
     }
 
-    private function formatValue($value, $format, $glue)
+    private function formatValue($value, $format, $glue): string
     {
         $formatCallable = is_callable($format);
 
diff --git a/src/Extension/Core/Type/ActionType.php b/src/Extension/Core/Type/ActionType.php
index ff7c526..bcca1c7 100644
--- a/src/Extension/Core/Type/ActionType.php
+++ b/src/Extension/Core/Type/ActionType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/BatchType.php b/src/Extension/Core/Type/BatchType.php
index 66dced7..13366af 100644
--- a/src/Extension/Core/Type/BatchType.php
+++ b/src/Extension/Core/Type/BatchType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/BooleanType.php b/src/Extension/Core/Type/BooleanType.php
index 5349ca0..c685833 100644
--- a/src/Extension/Core/Type/BooleanType.php
+++ b/src/Extension/Core/Type/BooleanType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/ColumnType.php b/src/Extension/Core/Type/ColumnType.php
index 57749ca..5d0820f 100644
--- a/src/Extension/Core/Type/ColumnType.php
+++ b/src/Extension/Core/Type/ColumnType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -94,12 +94,12 @@ public function getParent()
      *
      * @return string The prefix of the template block name
      */
-    public function getBlockPrefix()
+    public function getBlockPrefix(): string
     {
         return StringUtil::fqcnToBlockPrefix(get_class($this));
     }
 
-    private function createDataProvider(ColumnInterface $column)
+    private function createDataProvider(ColumnInterface $column): \Closure
     {
         return function ($data) use ($column) {
             $path = null;
diff --git a/src/Extension/Core/Type/CompoundColumnType.php b/src/Extension/Core/Type/CompoundColumnType.php
index 21adddc..9ffe580 100644
--- a/src/Extension/Core/Type/CompoundColumnType.php
+++ b/src/Extension/Core/Type/CompoundColumnType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/DateTimeType.php b/src/Extension/Core/Type/DateTimeType.php
index b99bd01..7178f30 100644
--- a/src/Extension/Core/Type/DateTimeType.php
+++ b/src/Extension/Core/Type/DateTimeType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/MoneyType.php b/src/Extension/Core/Type/MoneyType.php
index 40e219f..23aae8e 100644
--- a/src/Extension/Core/Type/MoneyType.php
+++ b/src/Extension/Core/Type/MoneyType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/NumberType.php b/src/Extension/Core/Type/NumberType.php
index 292d239..c615fea 100644
--- a/src/Extension/Core/Type/NumberType.php
+++ b/src/Extension/Core/Type/NumberType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/Type/TextType.php b/src/Extension/Core/Type/TextType.php
index 985cab8..5f78355 100644
--- a/src/Extension/Core/Type/TextType.php
+++ b/src/Extension/Core/Type/TextType.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Extension/Core/TypeExtension/ColumnOrderExtension.php b/src/Extension/Core/TypeExtension/ColumnOrderExtension.php
index 946fa4e..c03cb57 100644
--- a/src/Extension/Core/TypeExtension/ColumnOrderExtension.php
+++ b/src/Extension/Core/TypeExtension/ColumnOrderExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -38,7 +38,7 @@ public function buildHeaderView(HeaderView $view, ColumnInterface $column, array
     /**
      * {@inheritdoc}
      */
-    public function getExtendedType()
+    public function getExtendedType(): string
     {
         return ColumnType::class;
     }
diff --git a/src/Extension/Core/TypeExtension/CompoundColumnOrderExtension.php b/src/Extension/Core/TypeExtension/CompoundColumnOrderExtension.php
index 6c8a185..8c443fe 100644
--- a/src/Extension/Core/TypeExtension/CompoundColumnOrderExtension.php
+++ b/src/Extension/Core/TypeExtension/CompoundColumnOrderExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -23,7 +23,7 @@ class CompoundColumnOrderExtension extends ColumnOrderExtension
     /**
      * {@inheritdoc}
      */
-    public function getExtendedType()
+    public function getExtendedType(): string
     {
         return CompoundColumnType::class;
     }
diff --git a/src/PreloadedExtension.php b/src/PreloadedExtension.php
index 0fc600f..f166208 100644
--- a/src/PreloadedExtension.php
+++ b/src/PreloadedExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/src/Test/ColumnTypeTestCase.php b/src/Test/ColumnTypeTestCase.php
index 9966227..3294e27 100644
--- a/src/Test/ColumnTypeTestCase.php
+++ b/src/Test/ColumnTypeTestCase.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -88,5 +88,5 @@ protected function assertCellValueNotEquals($expectedValue, $data, array $option
         $this->assertNotEquals($expectedValue, $view->value);
     }
 
-    abstract protected function getTestedType();
+    abstract protected function getTestedType(): string;
 }
diff --git a/src/Test/DatagridIntegrationTestCase.php b/src/Test/DatagridIntegrationTestCase.php
index a65c90f..52333d3 100644
--- a/src/Test/DatagridIntegrationTestCase.php
+++ b/src/Test/DatagridIntegrationTestCase.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -34,7 +34,7 @@ protected function setUp()
         $this->factory = new DatagridFactory($typesRegistry);
     }
 
-    protected function getExtensions()
+    protected function getExtensions(): array
     {
         return [];
     }
diff --git a/src/Test/DatagridPerformanceTestCase.php b/src/Test/DatagridPerformanceTestCase.php
index c679125..13c83a9 100644
--- a/src/Test/DatagridPerformanceTestCase.php
+++ b/src/Test/DatagridPerformanceTestCase.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -52,7 +52,7 @@ protected function runTest()
      *
      * @throws \InvalidArgumentException
      */
-    public function setMaxRunningTime($maxRunningTime)
+    public function setMaxRunningTime(int $maxRunningTime)
     {
         if ($maxRunningTime >= 0) {
             $this->maxRunningTime = $maxRunningTime;
@@ -64,7 +64,7 @@ public function setMaxRunningTime($maxRunningTime)
     /**
      * @return int
      */
-    public function getMaxRunningTime()
+    public function getMaxRunningTime(): int
     {
         return $this->maxRunningTime;
     }
diff --git a/src/Util/StringUtil.php b/src/Util/StringUtil.php
index bb6fea7..9f1e5ff 100644
--- a/src/Util/StringUtil.php
+++ b/src/Util/StringUtil.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -31,7 +31,7 @@ private function __construct()
      *
      * @return string
      */
-    public static function trim($string)
+    public static function trim(string $string): string
     {
         if (null !== $result = @preg_replace('/^[\pZ\p{Cc}]+|[\pZ\p{Cc}]+$/u', '', $string)) {
             return $result;
@@ -47,7 +47,7 @@ public static function trim($string)
      *
      * @return string|null The block prefix or null if not a valid FQCN
      */
-    public static function fqcnToBlockPrefix($fqcn)
+    public static function fqcnToBlockPrefix(string $fqcn): string
     {
         // Non-greedy ("+?") to match "type" suffix, if present
         if (preg_match('~([^\\\\]+?)(type)?$~i', $fqcn, $matches)) {
diff --git a/tests/DatagridBuilderTest.php b/tests/DatagridBuilderTest.php
index ed56a3b..7bab29b 100644
--- a/tests/DatagridBuilderTest.php
+++ b/tests/DatagridBuilderTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/DatagridFactoryTest.php b/tests/DatagridFactoryTest.php
index 137f281..0b44726 100644
--- a/tests/DatagridFactoryTest.php
+++ b/tests/DatagridFactoryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/DatagridPerformanceTest.php b/tests/DatagridPerformanceTest.php
index 1b41c4f..f35e056 100644
--- a/tests/DatagridPerformanceTest.php
+++ b/tests/DatagridPerformanceTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/DatagridRowViewTest.php b/tests/DatagridRowViewTest.php
index e939dd6..450163b 100644
--- a/tests/DatagridRowViewTest.php
+++ b/tests/DatagridRowViewTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/DatagridTest.php b/tests/DatagridTest.php
index f5c97a8..40738c7 100644
--- a/tests/DatagridTest.php
+++ b/tests/DatagridTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/DatagridViewTest.php b/tests/DatagridViewTest.php
index fac067e..110ba64 100644
--- a/tests/DatagridViewTest.php
+++ b/tests/DatagridViewTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/ArrayToDateTimeTransformerTest.php b/tests/Extension/Core/DataTransformer/ArrayToDateTimeTransformerTest.php
index 736b9c9..2027642 100644
--- a/tests/Extension/Core/DataTransformer/ArrayToDateTimeTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/ArrayToDateTimeTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -32,12 +32,12 @@ public function testTransform()
         $transformer = new ArrayToDateTimeTransformer('UTC', 'UTC');
 
         $input = [
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ];
 
         $output = new \DateTime('2010-02-03 04:05:06 UTC');
@@ -50,12 +50,12 @@ public function testTransformWithSomeZero()
         $transformer = new ArrayToDateTimeTransformer('UTC', 'UTC');
 
         $input = [
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '0',
-            'second' => '0',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 0,
+            'second' => 0,
         ];
 
         $output = new \DateTime('2010-02-03 04:00:00 UTC');
@@ -99,11 +99,11 @@ public function testTransformPartiallyEmptyYear()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -114,11 +114,11 @@ public function testTransformPartiallyEmptyMonth()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -129,11 +129,11 @@ public function testTransformPartiallyEmptyDay()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -144,11 +144,11 @@ public function testTransformPartiallyEmptyHour()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -159,11 +159,11 @@ public function testTransformPartiallyEmptyMinute()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'second' => 6,
         ]);
     }
 
@@ -174,11 +174,11 @@ public function testTransformPartiallyEmptySecond()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
         ]);
     }
 
@@ -194,12 +194,12 @@ public function testTransformDifferentTimezones()
         $transformer = new ArrayToDateTimeTransformer('America/New_York', 'Asia/Hong_Kong');
 
         $input = [
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ];
 
         $output = new \DateTime('2010-02-03 04:05:06 Asia/Hong_Kong');
@@ -213,12 +213,12 @@ public function testTransformToDifferentTimezone()
         $transformer = new ArrayToDateTimeTransformer('Asia/Hong_Kong', 'UTC');
 
         $input = [
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ];
 
         $output = new \DateTime('2010-02-03 04:05:06 UTC');
@@ -243,12 +243,12 @@ public function testTransformWithNegativeYear()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '-1',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => -1,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -259,12 +259,12 @@ public function testTransformWithNegativeMonth()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '-1',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => -1,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -275,12 +275,12 @@ public function testTransformWithNegativeDay()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '-1',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => -1,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -291,12 +291,12 @@ public function testTransformWithNegativeHour()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '-1',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => -1,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -307,12 +307,12 @@ public function testTransformWithNegativeMinute()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '-1',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => -1,
+            'second' => 6,
         ]);
     }
 
@@ -323,12 +323,12 @@ public function testTransformWithNegativeSecond()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '-1',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => -1,
         ]);
     }
 
@@ -339,12 +339,12 @@ public function testTransformWithInvalidMonth()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '13',
-            'day' => '3',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 13,
+            'day' => 3,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -355,12 +355,12 @@ public function testTransformWithInvalidDay()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
-            'day' => '31',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'year' => 2010,
+            'month' => 2,
+            'day' => 31,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -371,12 +371,12 @@ public function testTransformWithStringDay()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
-            'month' => '2',
+            'year' => 2010,
+            'month' => 2,
             'day' => 'bazinga',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -387,12 +387,12 @@ public function testTransformWithStringMonth()
     {
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
-            'year' => '2010',
+            'year' => 2010,
             'month' => 'bazinga',
-            'day' => '31',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'day' => 31,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 
@@ -404,11 +404,11 @@ public function testTransformWithStringYear()
         $transformer = new ArrayToDateTimeTransformer();
         $transformer->transform([
             'year' => 'bazinga',
-            'month' => '2',
-            'day' => '31',
-            'hour' => '4',
-            'minute' => '5',
-            'second' => '6',
+            'month' => 2,
+            'day' => 31,
+            'hour' => 4,
+            'minute' => 5,
+            'second' => 6,
         ]);
     }
 }
diff --git a/tests/Extension/Core/DataTransformer/DateTimeTestCase.php b/tests/Extension/Core/DataTransformer/DateTimeTestCase.php
index 392e0a7..afaa5be 100644
--- a/tests/Extension/Core/DataTransformer/DateTimeTestCase.php
+++ b/tests/Extension/Core/DataTransformer/DateTimeTestCase.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformerTest.php b/tests/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformerTest.php
index 06fd782..4da2129 100644
--- a/tests/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/DateTimeToLocalizedStringTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/EmptyValueTransformerTest.php b/tests/Extension/Core/DataTransformer/EmptyValueTransformerTest.php
index e4fd8c5..10c0d78 100644
--- a/tests/Extension/Core/DataTransformer/EmptyValueTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/EmptyValueTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformerTest.php b/tests/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformerTest.php
index bfab8a2..e631b26 100644
--- a/tests/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php b/tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
index be37150..cf3dcd1 100644
--- a/tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/StringToDateTimeTransformerTest.php b/tests/Extension/Core/DataTransformer/StringToDateTimeTransformerTest.php
index 9d7d7a2..5b05fe9 100644
--- a/tests/Extension/Core/DataTransformer/StringToDateTimeTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/StringToDateTimeTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/TimestampToDateTimeTransformerTest.php b/tests/Extension/Core/DataTransformer/TimestampToDateTimeTransformerTest.php
index 228cd65..424342f 100644
--- a/tests/Extension/Core/DataTransformer/TimestampToDateTimeTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/TimestampToDateTimeTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/DataTransformer/ValueFormatTransformerTest.php b/tests/Extension/Core/DataTransformer/ValueFormatTransformerTest.php
index 60e9af0..efae03d 100644
--- a/tests/Extension/Core/DataTransformer/ValueFormatTransformerTest.php
+++ b/tests/Extension/Core/DataTransformer/ValueFormatTransformerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/Type/ActionTypeTest.php b/tests/Extension/Core/Type/ActionTypeTest.php
index b2a1a4f..1fdec98 100644
--- a/tests/Extension/Core/Type/ActionTypeTest.php
+++ b/tests/Extension/Core/Type/ActionTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -15,7 +15,7 @@
 
 class ActionTypeTest extends BaseTypeTest
 {
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return ActionType::class;
     }
diff --git a/tests/Extension/Core/Type/BaseTypeTest.php b/tests/Extension/Core/Type/BaseTypeTest.php
index cb08bba..aa0db51 100644
--- a/tests/Extension/Core/Type/BaseTypeTest.php
+++ b/tests/Extension/Core/Type/BaseTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Extension/Core/Type/BooleanTest.php b/tests/Extension/Core/Type/BooleanTest.php
index 8705973..b47c6d5 100644
--- a/tests/Extension/Core/Type/BooleanTest.php
+++ b/tests/Extension/Core/Type/BooleanTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -15,7 +15,7 @@
 
 class BooleanTest extends BaseTypeTest
 {
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return BooleanType::class;
     }
diff --git a/tests/Extension/Core/Type/ColumnTypeTest.php b/tests/Extension/Core/Type/ColumnTypeTest.php
index 02dfdf0..fa8711f 100644
--- a/tests/Extension/Core/Type/ColumnTypeTest.php
+++ b/tests/Extension/Core/Type/ColumnTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -81,7 +81,7 @@ public function testAutoConfigurationDataProviderFailsForUnsupportedPath()
         $datagrid->createView();
     }
 
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return ColumnType::class;
     }
diff --git a/tests/Extension/Core/Type/CompoundColumnTypeTest.php b/tests/Extension/Core/Type/CompoundColumnTypeTest.php
index 9ecd5d1..70c724e 100644
--- a/tests/Extension/Core/Type/CompoundColumnTypeTest.php
+++ b/tests/Extension/Core/Type/CompoundColumnTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -20,7 +20,7 @@
 
 class CompoundColumnTypeTest extends BaseTypeTest
 {
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return CompoundColumnType::class;
     }
diff --git a/tests/Extension/Core/Type/DateTimeTypeTest.php b/tests/Extension/Core/Type/DateTimeTypeTest.php
index bd26928..47811c0 100644
--- a/tests/Extension/Core/Type/DateTimeTypeTest.php
+++ b/tests/Extension/Core/Type/DateTimeTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -42,7 +42,7 @@ public function testPassLabelToView()
         $this->assertSame('My label', $view->label);
     }
 
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return DateTimeType::class;
     }
diff --git a/tests/Extension/Core/Type/MoneyTypeTest.php b/tests/Extension/Core/Type/MoneyTypeTest.php
index ff5c9fb..b26765e 100644
--- a/tests/Extension/Core/Type/MoneyTypeTest.php
+++ b/tests/Extension/Core/Type/MoneyTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -16,7 +16,7 @@
 
 class MoneyTypeTest extends BaseTypeTest
 {
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return MoneyType::class;
     }
diff --git a/tests/Extension/Core/Type/NumberTypeTest.php b/tests/Extension/Core/Type/NumberTypeTest.php
index 3115b6c..965aa98 100644
--- a/tests/Extension/Core/Type/NumberTypeTest.php
+++ b/tests/Extension/Core/Type/NumberTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -26,7 +26,7 @@ protected function setUp()
         \Locale::setDefault('de_DE');
     }
 
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return NumberType::class;
     }
diff --git a/tests/Extension/Core/Type/TextTypeTest.php b/tests/Extension/Core/Type/TextTypeTest.php
index 788d32d..f51d4ee 100644
--- a/tests/Extension/Core/Type/TextTypeTest.php
+++ b/tests/Extension/Core/Type/TextTypeTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
@@ -92,7 +92,7 @@ public function testEmptyValueAsArrayOption()
         $this->assertCellValueEquals(' - foo - , - ?2 - ', $data, $options);
     }
 
-    protected function getTestedType()
+    protected function getTestedType(): string
     {
         return TextType::class;
     }
diff --git a/tests/Fixtures/Entity.php b/tests/Fixtures/Entity.php
index 4acc301..e18fee9 100644
--- a/tests/Fixtures/Entity.php
+++ b/tests/Fixtures/Entity.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Fixtures/EntityManagerMock.php b/tests/Fixtures/EntityManagerMock.php
index e73a72c..3e04f2c 100644
--- a/tests/Fixtures/EntityManagerMock.php
+++ b/tests/Fixtures/EntityManagerMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Fixtures/EntityMapper.php b/tests/Fixtures/EntityMapper.php
index 8cfc232..beadf5a 100644
--- a/tests/Fixtures/EntityMapper.php
+++ b/tests/Fixtures/EntityMapper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Fixtures/EntityRepositoryMock.php b/tests/Fixtures/EntityRepositoryMock.php
index 406177f..41af8d2 100644
--- a/tests/Fixtures/EntityRepositoryMock.php
+++ b/tests/Fixtures/EntityRepositoryMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Fixtures/EntityTree.php b/tests/Fixtures/EntityTree.php
index edc3a91..633dcf0 100644
--- a/tests/Fixtures/EntityTree.php
+++ b/tests/Fixtures/EntityTree.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.
diff --git a/tests/Fixtures/EventManagerMock.php b/tests/Fixtures/EventManagerMock.php
index 0c1b9ec..c56980f 100644
--- a/tests/Fixtures/EventManagerMock.php
+++ b/tests/Fixtures/EventManagerMock.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the RollerworksDatagrid package.