diff --git a/tox.ini b/tox.ini
index 9722f0b0..add34820 100644
--- a/tox.ini
+++ b/tox.ini
@@ -37,3 +37,6 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 ignore = E125
 show-source = true
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
+# F821 undefined name 'unicode'
+# if isinstance(config, str) or isinstance(config, unicode):
+builtins = unicode