diff --git a/gertty/app.py b/gertty/app.py
index 1edaa0d..edf6b48 100644
--- a/gertty/app.py
+++ b/gertty/app.py
@@ -27,6 +27,7 @@ import threading
 import warnings
 import webbrowser
 
+import six
 from six.moves import queue
 from six.moves.urllib import parse as urlparse
 import sqlalchemy.exc