diff --git a/src/OverblogGraphQLBundle.php b/src/OverblogGraphQLBundle.php
index 3850ca908..80be31365 100644
--- a/src/OverblogGraphQLBundle.php
+++ b/src/OverblogGraphQLBundle.php
@@ -52,7 +52,7 @@ public function build(ContainerBuilder $container): void
         $container->addCompilerPass(new ResolverTaggedServiceMappingPass(), PassConfig::TYPE_BEFORE_REMOVING);
     }
 
-    public function getContainerExtension()
+    public function getContainerExtension(): ?ExtensionInterface
     {
         if (!$this->extension instanceof ExtensionInterface) {
             $this->extension = new OverblogGraphQLExtension();