diff --git a/tox.ini b/tox.ini
index 7a0d32c97..a85a435f9 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,10 +1,11 @@
 [tox]
-envlist = py27, pypy, py34, py35
+envlist = py27, pypy, py33, py34, py35
 
 [testenv]
 basepython =
     py27: {env:TOXPYTHON:python2.7}
     pypy: {env:TOXPYTHON:pypy}
+    py33: {env:TOXPYTHON:python3.3}
     py34: {env:TOXPYTHON:python3.4}
     py35: {env:TOXPYTHON:python3.5}
 deps =