diff --git a/tox.ini b/tox.ini
index 9509418..69d33fb 100644
--- a/tox.ini
+++ b/tox.ini
@@ -27,7 +27,7 @@ deps =
   coverage
   pytest-cov
   pytest-django
-  mock
+  mock<4
   pytest>=3.3.0
   lxml
   cssselect