diff --git a/tox.ini b/tox.ini
index b9298f3a..1952b093 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,7 +4,7 @@ envlist = py3, pep8, doc
 [testenv]
 basepython = python3
 commands=
-    python -bb -Wd -X faulthandler runtests.py
+    python -bb -Werror -X faulthandler runtests.py
 
 [testenv:pep8]
 allowlist_externals = sh