diff --git a/setup.cfg b/setup.cfg
index 0932c49..15e8324 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -29,7 +29,7 @@ trafficlight = py.typed
 [options.extras_require]
 dev =
   # for tests
-  tox
+  tox == 3.28.0
   # for type checking
   mypy == 0.940
   # for linting