diff --git a/buildtrigger/githubhandler.py b/buildtrigger/githubhandler.py
index 7c47df4ff..a6df8a979 100644
--- a/buildtrigger/githubhandler.py
+++ b/buildtrigger/githubhandler.py
@@ -362,8 +362,14 @@ class GithubBuildTrigger(BuildTriggerHandler):
   def load_dockerfile_contents(self):
     config = self.config
     gh_client = self._get_client()
-
     source = config['build_source']
+
+    try:
+      repo = gh_client.get_repo(source)
+    except GithubException as ghe:
+      message = ghe.data.get('message', 'Unable to list contents of repository: %s' % source)
+      raise RepositoryReadException(message)
+
     path = self.get_dockerfile_path()
     try:
       file_info = repo.get_file_contents(path)