diff --git a/tox.ini b/tox.ini
index 7c7e9457..684056b8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,7 @@ envlist=
 [testenv]
 deps=
     unittest2
-    virtualenv==20.0.23
+extras = yaml
 commands=
     unit2 discover -s tests/unit -p test_*_py3.py