diff --git a/tox.ini b/tox.ini
index 578e3b5..ad152a4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -81,6 +81,7 @@ commands =
 deps =
     pycrypto==2.6
     pyopenssl==0.14
+passenv = GOOGLE_* OAUTH2CLIENT_* TRAVIS*
 
 [testenv:system-tests3]
 basepython =
@@ -90,3 +91,4 @@ commands =
 deps =
     pycrypto==2.6
     pyopenssl==0.14
+passenv = {[testenv:system-tests]passenv}