diff --git a/tox.ini b/tox.ini
index 443448ca..51233eb2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -96,6 +96,7 @@ setenv =
        lang_utf8: LANG=en_US.utf-8
        # tox's parser chokes if all the setenv entries are conditional.
        DUMMY=dummy
+       {py2,py26,py27,py3,py32,py33,py34}-no-ext: TORNADO_EXTENSION=0
 
 # All non-comment lines but the last must end in a backslash.
 # Tox filters line-by-line based on the environment name.