diff --git a/endpoints/trigger.py b/endpoints/trigger.py
index 61c5e7ef8..289eb5937 100644
--- a/endpoints/trigger.py
+++ b/endpoints/trigger.py
@@ -403,12 +403,13 @@ class GithubBuildTrigger(BuildTrigger):
 
       gh_client = self._get_client(auth_token)
       repo = gh_client.get_repo(source)
-      master = repo.get_branch(repo.default_branch)
-      master_sha = master.commit.sha
-      short_sha = GithubBuildTrigger.get_display_name(master_sha)
-      ref = 'refs/heads/%s' % (run_parameters.get('branch_name') or repo.default_branch)
+      branch_name = run_parameters.get('branch_name') or repo.default_branch
+      branch = repo.get_branch(branch_name)
+      branch_sha = branch.commit.sha
+      short_sha = GithubBuildTrigger.get_display_name(branch_sha)
+      ref = 'refs/heads/%s' % (branch_name)
 
-      return self._prepare_build(config, repo, master_sha, short_sha, ref)
+      return self._prepare_build(config, repo, branch_sha, short_sha, ref)
     except GithubException as ghe:
       raise TriggerStartException(ghe.data['message'])