diff --git a/Tests/Application/Kernel.php b/Tests/Application/Kernel.php
index f58f486e..bd6d10c9 100644
--- a/Tests/Application/Kernel.php
+++ b/Tests/Application/Kernel.php
@@ -43,7 +43,7 @@ public function registerBundles(): iterable
         return $bundles;
     }
 
-    public function registerContainerConfiguration(LoaderInterface $loader)
+    public function registerContainerConfiguration(LoaderInterface $loader): void
     {
         parent::registerContainerConfiguration($loader);
         $loader->load(__DIR__ . '/config/config_' . $this->getContext() . '.yml');