diff --git a/data/model/image.py b/data/model/image.py
index 2fc8f837d..031f4a660 100644
--- a/data/model/image.py
+++ b/data/model/image.py
@@ -71,7 +71,10 @@ def _get_parent_images(namespace_name, repository_name, image_obj, include_place
                                                   filter_to_parents)
 
   id_to_image = {unicode(image.id): image for image in parents}
-  return [id_to_image[parent_id] for parent_id in reversed(parent_db_ids)]
+  try:
+    return [id_to_image[parent_id] for parent_id in reversed(parent_db_ids)]
+  except KeyError:
+    raise DataModelException('Unknown parent image')
 
 
 def get_repo_image(namespace_name, repository_name, docker_image_id):