Traverse the method resolution order when mapping serializer fields.

rest_framework/serializers.py

@@ -904,11 +904,9 @@ class ModelSerializer(Serializer):
             for attribute in attributes:
                 kwargs.update({attribute: getattr(model_field, attribute)})
 
-        try:
-            return self.field_mapping[model_field.__class__](**kwargs)
-        except KeyError:
-            for model_field_class, serializer_field_class in self.field_mapping.items():
-                if isinstance(model_field, model_field_class):
+        for model_field_baseclass in inspect.getmro(model_field.__class__):
+            serializer_field_class = self.field_mapping.get(model_field_baseclass)
+            if serializer_field_class:
                 return serializer_field_class(**kwargs)
         return ModelField(model_field=model_field, **kwargs)