diff --git a/tox.ini b/tox.ini
index fa8a840..dcc3983 100644
--- a/tox.ini
+++ b/tox.ini
@@ -34,7 +34,7 @@ deps =
   pytest-cov
   pytest-django
   pytest
-  mock
+  mock<4
   django-webtest<1.9.3
   psycopg2
   pyquery