diff --git a/endpoints/registry.py b/endpoints/registry.py
index 5699f0db2..2327ffde6 100644
--- a/endpoints/registry.py
+++ b/endpoints/registry.py
@@ -278,6 +278,9 @@ def put_image_checksum(namespace, repository, image_id):
 
   profile.debug('Looking up repo image')
   repo_image = model.get_repo_image(namespace, repository, image_id)
+  if not repo_image or not repo_image.storage:
+    abort(404, 'Image not found: %(image_id)s', issue='unknown-image', image_id=image_id)
+
   uuid = repo_image.storage.uuid
 
   profile.debug('Looking up repo layer data')