diff --git a/tox.ini b/tox.ini
index 6609529..a88a585 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,7 +6,7 @@ setenv = VIRTUAL_ENV={envdir}
 
 [testenv:pep8]
 deps = argparse
-       hacking
+       hacking<0.6
 commands = flake8
 
 [testenv:sdist]