diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 6caae9242..2edb24d6a 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -380,6 +380,8 @@ class WritableField(Field):
         """
         return value
 
+    def save_serializer_data(self, instance, field_name, data):
+        setattr(instance, field_name, data)
 
 class ModelField(WritableField):
     """
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 43d339da0..73f0fd611 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -1013,7 +1013,8 @@ class ModelSerializer(Serializer):
 
         if getattr(obj, '_m2m_data', None):
             for accessor_name, object_list in obj._m2m_data.items():
-                setattr(obj, accessor_name, object_list)
+                field = self.fields[accessor_name]
+                field.save_serializer_data(obj, accessor_name, object_list)
             del(obj._m2m_data)
 
         if getattr(obj, '_related_data', None):