diff --git a/service_container.rst b/service_container.rst
index 1f3a248dbe5..4c608f903d7 100644
--- a/service_container.rst
+++ b/service_container.rst
@@ -1436,7 +1436,7 @@ You also have a service that defines many methods and one of them is the same
     // src/Service/MessageUtils.php
     namespace App\Service;
 
-    class MessageUtils
+    class MessageUtils implements MessageFormatterInterface
     {
         // other methods...