diff --git a/src/Caching/IgnoreCacheHandler.php b/src/Caching/IgnoreCacheHandler.php
index f6b79d2..5b2126f 100644
--- a/src/Caching/IgnoreCacheHandler.php
+++ b/src/Caching/IgnoreCacheHandler.php
@@ -10,7 +10,7 @@
 
 class IgnoreCacheHandler
 {
-    public function execute(AssetManager $assetManager)
+    public function execute(AssetManager $assetManager): void
     {
         /** @var IgnorePluginCacheInterface[] $handlers */
         $handlers = [