diff --git a/tox.ini b/tox.ini
index f86ec4b..0825210 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,6 +7,7 @@
 envlist = py27, py34, py35, py36, pypy
 
 [testenv]
+usedevelop = true
 commands = py.test -vv
 deps =
     future