diff --git a/tox.ini b/tox.ini
index 8ded281d..441cca90 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,7 +14,7 @@ deps =
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
 commands = ostestr {posargs}
-passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY OS_*
+passenv = http_proxy,HTTP_PROXY,https_proxy,HTTPS_PROXY,no_proxy,NO_PROXY,OS_*
 
 [testenv:venv]
 commands = {posargs}