diff --git a/shotgun_api3/lib/mockgun/mockgun.py b/shotgun_api3/lib/mockgun/mockgun.py
index 6a2f79de..eab05f88 100644
--- a/shotgun_api3/lib/mockgun/mockgun.py
+++ b/shotgun_api3/lib/mockgun/mockgun.py
@@ -496,6 +496,7 @@ def _validate_entity_data(self, entity_type, data):
                                    "percent": int,
                                    "text": six.string_types,
                                    "serializable": dict,
+                                   "entity_type": six.string_types,
                                    "date": datetime.date,
                                    "date_time": datetime.datetime,
                                    "list": six.string_types,