diff --git a/buildtrigger/githubhandler.py b/buildtrigger/githubhandler.py
index d92d9530d..d60c802fb 100644
--- a/buildtrigger/githubhandler.py
+++ b/buildtrigger/githubhandler.py
@@ -118,7 +118,8 @@ def get_transformed_webhook_payload(gh_payload, default_branch=None, lookup_user
 
   # Note: GitHub doesn't always return the extra information for users, so we do the lookup
   # manually if possible.
-  if lookup_user and not payload.get('head_commit.author.html_url'):
+  if (lookup_user and not payload.get('head_commit.author.html_url') and
+      payload.get('head_commit.author.username')):
     author_info = lookup_user(payload['head_commit.author.username'])
     if author_info:
       config['commit_info.author.url'] = author_info['html_url']
diff --git a/test/test_prepare_trigger.py b/test/test_prepare_trigger.py
index b2ca6d7e8..54c00454d 100644
--- a/test/test_prepare_trigger.py
+++ b/test/test_prepare_trigger.py
@@ -171,6 +171,30 @@ class TestPrepareTrigger(unittest.TestCase):
     self.assertSchema('github_webhook', expected, gh_webhook, lookup_user=lookup_user)
 
 
+  def test_github_webhook_payload_missing_fields_with_lookup(self):
+    expected = {
+      'commit': u'410f4cdf8ff09b87f245b13845e8497f90b90a4c',
+      'ref': u'refs/heads/master',
+      'git_url': u'git@github.com:josephschorr/anothertest.git',
+      'commit_info': {
+        'url': u'https://github.com/josephschorr/anothertest/commit/410f4cdf8ff09b87f245b13845e8497f90b90a4c',
+        'date': u'2015-09-11T14:26:16-04:00',
+        'message': u'Update Dockerfile'
+      },
+    }
+
+    def lookup_user(username):
+      if not username:
+        raise Exception('Fail!')
+
+      return {
+        'html_url': 'http://github.com/josephschorr',
+        'avatar_url': 'http://some/avatar/url'
+      }
+
+    self.assertSchema('github_webhook_missing', expected, gh_webhook, lookup_user=lookup_user)
+
+
   def test_gitlab_webhook_payload(self):
     expected = {
       'commit': u'fb88379ee45de28a0a4590fddcbd8eff8b36026e',