diff --git a/tox.ini b/tox.ini
index cf89e41..85eafcd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py35,py36
+envlist = py33,py34,py35,py36
 skipsdist = True
 
 [testenv]