diff --git a/endpoints/trigger.py b/endpoints/trigger.py
index ab7aa9065..ae0b4b2b7 100644
--- a/endpoints/trigger.py
+++ b/endpoints/trigger.py
@@ -291,6 +291,9 @@ class GithubBuildTrigger(BuildTrigger):
       with tarfile.open(fileobj=tarball) as archive:
         tarball_subdir = archive.getnames()[0]
 
+      # Seek to position 0 to make boto multipart happy
+      tarball.seek(0)
+
       dockerfile_id = user_files.store_file(tarball, TARBALL_MIME)
 
     logger.debug('Successfully prepared job')