diff --git a/tox.ini b/tox.ini
index 55fb3a0..b22e533 100644
--- a/tox.ini
+++ b/tox.ini
@@ -16,6 +16,7 @@ deps =
     django22: django>=2.2,<2.3
     django30: django>=3.0,<3.1
     appdirs==1.4.3
+    six==1.14.0
     py27: mock==2.0.0
 
 [testenv:lint]