diff --git a/tox.ini b/tox.ini
index b1c678d..3da8626 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,6 +13,7 @@ setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = python setup.py testr --testr-args='{posargs}'
+whitelist_externals = flake8
 
 [testenv:pep8]
 commands = flake8