diff --git a/tox.ini b/tox.ini
index 99af832..fd5d24e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,6 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
+minversion = 1.6
 envlist = pep8, py27
 
 [testenv]