diff --git a/src/Types/GeometryCollection.php b/src/Types/GeometryCollection.php
index 35f093f7..264536d0 100755
--- a/src/Types/GeometryCollection.php
+++ b/src/Types/GeometryCollection.php
@@ -11,6 +11,7 @@
 use Illuminate\Contracts\Support\Arrayable;
 use InvalidArgumentException;
 use IteratorAggregate;
+use Traversable;
 
 class GeometryCollection extends Geometry implements IteratorAggregate, ArrayAccess, Arrayable, Countable
 {
@@ -87,22 +88,22 @@ public function toArray()
         return $this->items;
     }
 
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->items);
     }
 
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return isset($this->items[$offset]);
     }
 
-    public function offsetGet($offset)
+    public function offsetGet($offset): mixed
     {
         return $this->offsetExists($offset) ? $this->items[$offset] : null;
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->validateItemType($value);
 
@@ -113,12 +114,12 @@ public function offsetSet($offset, $value)
         }
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         unset($this->items[$offset]);
     }
 
-    public function count()
+    public function count(): int
     {
         return count($this->items);
     }
@@ -146,7 +147,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\GeometryCollection
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         $geometries = [];
         foreach ($this->items as $geometry) {
diff --git a/src/Types/LineString.php b/src/Types/LineString.php
index 1cc4a410..09017149 100644
--- a/src/Types/LineString.php
+++ b/src/Types/LineString.php
@@ -65,7 +65,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\LineString
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         $points = [];
         foreach ($this->items as $point) {
diff --git a/src/Types/MultiLineString.php b/src/Types/MultiLineString.php
index 62c4d576..02debf41 100644
--- a/src/Types/MultiLineString.php
+++ b/src/Types/MultiLineString.php
@@ -49,7 +49,7 @@ public function __toString()
         }, $this->getLineStrings()));
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->validateItemType($value);
 
@@ -83,7 +83,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\MultiLineString
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         $lineStrings = [];
 
diff --git a/src/Types/MultiPoint.php b/src/Types/MultiPoint.php
index 752967eb..eb98cfd8 100644
--- a/src/Types/MultiPoint.php
+++ b/src/Types/MultiPoint.php
@@ -69,7 +69,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\MultiPoint
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         $points = [];
         foreach ($this->items as $point) {
diff --git a/src/Types/MultiPolygon.php b/src/Types/MultiPolygon.php
index cdea3a9c..4f317635 100644
--- a/src/Types/MultiPolygon.php
+++ b/src/Types/MultiPolygon.php
@@ -89,7 +89,7 @@ protected static function assembleParts(array $parts)
         return $polygons;
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->validateItemType($value);
 
@@ -127,7 +127,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\MultiPolygon
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         $polygons = [];
         foreach ($this->items as $polygon) {
diff --git a/src/Types/Point.php b/src/Types/Point.php
index d424ec5e..860d25e8 100644
--- a/src/Types/Point.php
+++ b/src/Types/Point.php
@@ -92,7 +92,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\Point
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         return new GeoJsonPoint([$this->getLng(), $this->getLat()]);
     }
diff --git a/src/Types/PointCollection.php b/src/Types/PointCollection.php
index 30d1b8de..862e80aa 100755
--- a/src/Types/PointCollection.php
+++ b/src/Types/PointCollection.php
@@ -21,7 +21,7 @@ public function toPairList()
         }, $this->items));
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->validateItemType($value);
 
diff --git a/src/Types/Polygon.php b/src/Types/Polygon.php
index 9c10cecc..acd6da10 100644
--- a/src/Types/Polygon.php
+++ b/src/Types/Polygon.php
@@ -40,7 +40,7 @@ public static function fromJson($geoJson)
      *
      * @return \GeoJson\Geometry\Polygon
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         $linearRings = [];
         foreach ($this->items as $lineString) {