diff --git a/tox.ini b/tox.ini
index 4dc65f0..aa8ecf1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -76,7 +76,7 @@
     hypothesis
     mutmut
 commands =
-    mutmut run --paths-to-mutate "src/newlang/parse2,src/newlang/i18n.py"
+    mutmut {posargs:run --paths-to-mutate "src/newlang/parse2,src/newlang/i18n.py"}
 commands_post =
     mutmut results