diff --git a/notifier.rst b/notifier.rst
index 30893558654..b35db12f8ea 100644
--- a/notifier.rst
+++ b/notifier.rst
@@ -717,7 +717,8 @@ typical alert levels, which you can implement immediately using:
 
         # config/services.yaml
         services:
-            notifier.flash_message_importance_mapper: Symfony\Component\Notifier\FlashMessage\BootstrapFlashMessageImportanceMapper
+            notifier.flash_message_importance_mapper: 
+                class: Symfony\Component\Notifier\FlashMessage\BootstrapFlashMessageImportanceMapper
 
     .. code-block:: xml