diff --git a/notebook/base/handlers.py b/notebook/base/handlers.py
index 63d90446b9..798456caec 100755
--- a/notebook/base/handlers.py
+++ b/notebook/base/handlers.py
@@ -486,8 +486,10 @@ def write_error(self, status_code, **kwargs):
             e = exc_info[1]
             if isinstance(e, HTTPError):
                 reply['message'] = e.log_message or message
+                reply['reason'] = e.reason
             else:
                 reply['message'] = 'Unhandled error'
+                reply['reason'] = None
                 reply['traceback'] = ''.join(traceback.format_exception(*exc_info))
         self.log.warning(reply['message'])
         self.finish(json.dumps(reply))