1 files changed, 2 insertions, 0 deletions

diff --git a/.zuul.yaml b/.zuul.yaml
index 0ae7d9f..3b177d2 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -38,6 +38,8 @@
       tox_envlist: functional-py39
 
 - project:
+    vars:
+      ensure_tox_version: '<4'
     templates:
       - check-requirements
       - lib-forward-testing-python3