diff --git a/composer.json b/composer.json
index d6801c0..4f73d25 100644
--- a/composer.json
+++ b/composer.json
@@ -22,7 +22,7 @@
         }
     ],
     "require": {
-        "craftcms/cms": "^3.1",
+        "craftcms/cms": "^4.0.3",
         "guzzlehttp/guzzle": "^6.3 || ^7.2"
     },
     "autoload": {
diff --git a/src/CraftRecaptcha.php b/src/CraftRecaptcha.php
index 5cbf2e8..12ec2f9 100644
--- a/src/CraftRecaptcha.php
+++ b/src/CraftRecaptcha.php
@@ -65,7 +65,7 @@ class CraftRecaptcha extends Plugin
      *
      * @var string
      */
-    public $schemaVersion = '1.0.0';
+    public string $schemaVersion = '1.0.0';
 
     // Public Methods
     // =========================================================================
@@ -163,7 +163,7 @@ function (PluginEvent $event) {
      *
      * @return \craft\base\Model|null
      */
-    protected function createSettingsModel()
+    protected function createSettingsModel() : ? \craft\base\Model
     {
         return new Settings();
     }
diff --git a/src/models/Settings.php b/src/models/Settings.php
index b5beb69..e0a09c9 100644
--- a/src/models/Settings.php
+++ b/src/models/Settings.php
@@ -84,7 +84,7 @@ public function getSecretKey(): string
     return Craft::parseEnv($this->secretKey);
   }
 
-  public function behaviors()
+  public function behaviors() :array
   {
     return [
         'parser' => [
@@ -104,7 +104,7 @@ public function behaviors()
      *
      * @return array
      */
-    public function rules()
+    public function rules() :array
     {
         return [
             ['siteKey', 'string'],