diff --git a/tox.ini b/tox.ini
index cafecaca..84770c5c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -44,6 +44,7 @@ basepython =
     py26: python2.6
     py27: python2.7
 usedevelop = True
+passenv = *
 deps = pytest
 setenv =
     PLATFORMIO_SETTING_ENABLE_PROMPTS = False