diff --git a/tox.ini b/tox.ini
index 65d647a24e..28ad4e7a07 100644
--- a/tox.ini
+++ b/tox.ini
@@ -22,7 +22,7 @@ commands =
   flake8 {posargs}
   {toxinidir}/tools/config/check_uptodate.sh
   # Check that .po and .pot files are valid:
-  bash -c "find ironic -type f -regex '.*\.pot?' -print0|xargs --null -n 1 msgfmt --check-format -o /dev/null"
+  bash -c "find ironic -type f -regex '.*\.pot?' -print0|xargs -0 -n 1 msgfmt --check-format -o /dev/null"
 
 [testenv:cover]
 setenv = VIRTUAL_ENV={envdir}