diff --git a/tox.ini b/tox.ini
index 530e5b941..c90732b11 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,6 +2,7 @@
 envlist=flake8,py27,py34,py35,py36,pypy,du13,du12,du11
 
 [testenv]
+passenv = https_proxy http_proxy no_proxy
 deps=
     six
     pytest