diff --git a/tox.ini b/tox.ini
index a5feba6e77..2684fff316 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,6 +6,12 @@ skipsdist = True
 # env and ignore basepython inherited from [testenv] if we set
 # ignore_basepython_conflict.
 ignore_basepython_conflict = True
+# Cap setuptools via virtualenv to prevent compatibility issue with victoria
+# branch's upper constraint of pbr package (5.5.0). Tox is also needed to be
+# constrained for the 'inner' tox to be installed with the constrained venv.
+requires =
+  virtualenv<20.24.0
+  tox<4
 
 [testenv]
 basepython = python3