diff --git a/requirements/tox.txt b/requirements/tox.txt
index 4015c91e..2d947559 100644
--- a/requirements/tox.txt
+++ b/requirements/tox.txt
@@ -1,2 +1,2 @@
 # requirements for building and running tox
-tox>=3.3.0
+tox>=3.3.0,<4