diff --git a/tox.ini b/tox.ini
index 683eb509131..429dd6c0062 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 envlist = docs,py34,py27,pep8
-minversion = 2.3
+minversion = 2.3.1
 skipsdist = True
 
 [testenv]