diff --git a/phpstan.neon b/phpstan.neon
index a64d774..6d49eb4 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,5 @@
 parameters:
-  level: 5
+  level: 6
   paths:
     - src
 
diff --git a/src/ComposerScripts.php b/src/ComposerScripts.php
index 2ba7910..be43613 100644
--- a/src/ComposerScripts.php
+++ b/src/ComposerScripts.php
@@ -22,7 +22,7 @@ class ComposerScripts
      */
     protected static $vendorDir;
 
-    protected static function getBinDir(Event $event)
+    protected static function getBinDir(Event $event): string
     {
         if (!static::$binDir) {
             static::$binDir = realpath($event->getComposer()->getConfig()->get('bin-dir'));
@@ -31,7 +31,7 @@ protected static function getBinDir(Event $event)
         return static::$binDir;
     }
 
-    protected static function getVendorDir(Event $event)
+    protected static function getVendorDir(Event $event): string
     {
         if (!static::$vendorDir) {
             static::$vendorDir = realpath($event->getComposer()->getConfig()->get('vendor-dir'));
@@ -40,7 +40,7 @@ protected static function getVendorDir(Event $event)
         return static::$vendorDir;
     }
 
-    protected static function bootstrap(Event $event)
+    protected static function bootstrap(Event $event): void
     {
         require_once static::getVendorDir($event) . '/autoload.php';
     }