diff --git a/endpoints/api/trigger.py b/endpoints/api/trigger.py
index d44cb78a1..5ec5c4b0c 100644
--- a/endpoints/api/trigger.py
+++ b/endpoints/api/trigger.py
@@ -400,6 +400,14 @@ class ActivateBuildTrigger(RepositoryParamResource):
         'commit_sha': {
           'type': 'string',
           'description': '(Custom Only) If specified, the ref/SHA1 used to checkout a git repository.'
+        },
+        'refs': {
+          'type': 'array',
+          'description': '(SCM Only) If specified, the refs to build.'
+        },
+        'branch_name': {
+          'type': 'string',
+          'description': '(SCM Only) If specified, the branch to build.'
         }
       },
       'additionalProperties': False
diff --git a/test/test_api_usage.py b/test/test_api_usage.py
index 419d3ffc8..4ef0e406b 100644
--- a/test/test_api_usage.py
+++ b/test/test_api_usage.py
@@ -2989,6 +2989,13 @@ class TestBuildTriggers(ApiTestCase):
     build_obj = database.RepositoryBuild.get(database.RepositoryBuild.uuid == start_json['id'])
     self.assertEquals('bar', py_json.loads(build_obj.job_config)['trigger_metadata']['foo'])
 
+    # Start another manual build, with a ref.
+    start_json = self.postJsonResponse(ActivateBuildTrigger,
+                                       params=dict(repository=ADMIN_ACCESS_USER + '/simple',
+                                                   trigger_uuid=trigger.uuid),
+                                       data=dict(refs=[{'kind': 'branch', 'name': 'foobar'}]),
+                                       expected_code=201)
+
   def test_invalid_robot_account(self):
     self.login(ADMIN_ACCESS_USER)