diff --git a/sugar/activity/bundlebuilder.py b/sugar/activity/bundlebuilder.py
index 92d88220..d4e04e85 100644
--- a/sugar/activity/bundlebuilder.py
+++ b/sugar/activity/bundlebuilder.py
@@ -151,7 +151,7 @@ def cmd_uninstall(prefix):
         shutil.rmtree(path)
 
 def cmd_clean():
-    os.path.walk('.', delete_backups, None)
+    os.path.walk('.', _delete_backups, None)
 
 def start():
     if len(sys.argv) < 2: