diff --git a/tox.ini b/tox.ini
index a99de82d..6ad610a2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,7 +13,7 @@ deps =
   pytest
   cryptography
   python-dateutil
-  flask21: Flask>=2.1,<2.2
+  flask21: Flask>=2.1,<2.2;Werkzeug<3.0
 
 [testenv:mypy]
 commands =