diff --git a/tox.ini b/tox.ini
index cc2b24a..64889de 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,7 +28,7 @@ deps =
         pytest-freezegun
         django-webtest
         WebTest
-        mock
+        mock<4
 commands =
         py.test {env:COVERAGE:} {posargs:tests/}
         pylint: ./pylint.sh fargo/