diff --git a/tox.ini b/tox.ini
index ad152a4..54f6c33 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,6 +35,7 @@ commands =
 deps =
     {[testenv:cover]deps}
     coveralls
+passenv = {[testenv:system-tests]passenv}
 
 [testenv:docs]
 basepython = python2.7