diff --git a/tox.ini b/tox.ini
index e8a1b75..65a38ce 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,7 +2,7 @@
 envlist = docs, py38, py37, py36, py35, pypy3, deps
 
 [testenv]
-passenv = WHEELHOUSE PIP_FIND_LINKS PIP_WHEEL_DIR PIP_INDEX_URL
+passenv = WHEELHOUSE,PIP_FIND_LINKS,PIP_WHEEL_DIR,PIP_INDEX_URL
 setenv = PYTHONPATH = {toxinidir}
 deps = -r{toxinidir}/ci/requirements-tests.txt
 commands = pytest -v --flakes --cache-clear --basetemp={envtmpdir} {posargs}