diff --git a/tox.ini b/tox.ini
index 419df51..394b70e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,7 +18,7 @@ deps =
   pytest
   pylint
   pylint-django
-  mock
+  mock<4
   djangorestframework>=3.3,<3.8
 commands =
   py2: ./getlasso.sh