diff --git a/tox.ini b/tox.ini
index 50236788c4..ca70f1eb28 100644
--- a/tox.ini
+++ b/tox.ini
@@ -27,7 +27,7 @@ downloadcache = ~/cache/pip
 
 [testenv:pep8]
 commands =
-  flake8 swift test doc setup.py
+  flake8 {posargs:swift test doc setup.py}
   flake8 --filename=swift* bin
 
 [testenv:py3pep8]