diff --git a/Tests/Application/Kernel.php b/Tests/Application/Kernel.php
index b75ea4e2..56276f25 100644
--- a/Tests/Application/Kernel.php
+++ b/Tests/Application/Kernel.php
@@ -39,7 +39,7 @@ public function registerBundles(): iterable
         return $bundles;
     }
 
-    public function registerContainerConfiguration(LoaderInterface $loader)
+    public function registerContainerConfiguration(LoaderInterface $loader): void
     {
         parent::registerContainerConfiguration($loader);