diff --git a/components/serializer.rst b/components/serializer.rst
index e1f95df346a..319940027a3 100644
--- a/components/serializer.rst
+++ b/components/serializer.rst
@@ -724,7 +724,7 @@ When serializing, you can set a callback to format a specific object property::
 
     // all callback parameters are optional (you can omit the ones you don't use)
     $dateCallback = function ($innerObject, $outerObject, string $attributeName, string $format = null, array $context = []) {
-        return $innerObject instanceof \DateTime ? $innerObject->format(\DateTime::ISO8601) : '';
+        return $innerObject instanceof \DateTime ? $innerObject->format(\DateTime::ATOM) : '';
     };
 
     $defaultContext = [