--- a/taskcluster/taskgraph/actions/registry.py
+++ b/taskcluster/taskgraph/actions/registry.py
@@ -175,17 +175,17 @@ def register_callback_action(name, title
         @register_task_action(name, title, description, order, context, schema)
         def build_callback_action_task(parameters):
             if not available(parameters):
                 return None
 
             match = re.match(r'https://(hg.mozilla.org)/(.*?)/?$', parameters['head_repository'])
             if not match:
                 raise Exception('Unrecognized head_repository')
-            repo_scope = 'assume:repo:{}/{}:*'.format(
+            repo_scope = 'assume:repo:{}/{}:branch:default'.format(
                 match.group(1), match.group(2))
 
             task_group_id = os.environ.get('TASK_ID', slugid())
 
             template = os.path.join(GECKO, '.taskcluster.yml')
 
             with open(template, 'r') as f:
                 taskcluster_yml = yaml.safe_load(f)