diff --git a/components/serializer.rst b/components/serializer.rst
index 164a29edc0b..c4137e36a73 100644
--- a/components/serializer.rst
+++ b/components/serializer.rst
@@ -169,10 +169,11 @@ needs three parameters:
     Support for the ``allow_extra_attributes`` key in the context was introduced
     in Symfony 3.3.
 
-By default, additional attributes that are not mapped to the denormalized
-object will be ignored by the Serializer component. Set the ``allow_extra_attributes``
-key of the deserialization context to ``false`` to let the serializer throw
-an exception when additional attributes are passed::
+By default, additional attributes that are not mapped to the denormalized object
+will be ignored by the Serializer component. If you prefer to throw an exception
+when this happens, set the ``allow_extra_attributes`` context option to
+``false`` and provide an object that implements ``ClassMetadataFactoryInterface`
+when constructing the normalizer::
 
     $data = <<<EOF
     <person>
@@ -184,6 +185,9 @@ an exception when additional attributes are passed::
 
     // this will throw a Symfony\Component\Serializer\Exception\ExtraAttributesException
     // because "city" is not an attribute of the Person class
+    $classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
+    $normalizer = new ObjectNormalizer($classMetadataFactory);
+    $serializer = new Serializer(array($normalizer));
     $person = $serializer->deserialize($data, 'Acme\Person', 'xml', array(
         'allow_extra_attributes' => false,
     ));