diff --git a/doc/howto/custom_field_type.md b/doc/howto/custom_field_type.md
index 1c6250f3..67149d1a 100644
--- a/doc/howto/custom_field_type.md
+++ b/doc/howto/custom_field_type.md
@@ -58,6 +58,7 @@ class LandingPageGraphQLConfigurationPass implements CompilerPassInterface
             'definition_type' => 'MyCustomFieldDefinition',
             'value_resolver' => 'field.someProperty'
         ];
+        $container->setParameter('ezplatform_graphql.schema.content.mapping.field_definition_type', $mapping);
     }
 }
 ```
@@ -189,4 +190,4 @@ Two variables are available in the resolver's expression:
 - `field` is the current field, as an extension of the API's Field object that proxies properties requests to the Field Value
 - `content` is the resolved content item's `ContentInfo`.
 
-`RelationFieldValueBuilder` or `SelectionFieldValueBuilder` can be used as examples.
\ No newline at end of file
+`RelationFieldValueBuilder` or `SelectionFieldValueBuilder` can be used as examples.