diff --git a/.zuul.yaml b/.zuul.yaml
index c6e340e8e..565e3923d 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -1,4 +1,6 @@
 - project:
+    vars:
+      ensure_tox_version: '<4'
     templates:
       - check-requirements
       - lib-forward-testing-python3
diff --git a/tox.ini b/tox.ini
index dc94d8bf9..a3ae02351 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,6 @@
 [tox]
 minversion = 3.18.0
+requires = tox<4
 skipsdist = True
 # python runtimes: https://governance.openstack.org/tc/reference/runtimes/ussuri.html
 envlist = py3,pep8