diff --git a/tox.ini b/tox.ini
index be6cbbb..8fe45b2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,6 +10,7 @@ setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
+passenv = *_proxy *_PROXY
 
 [testenv:venv]
 commands = {posargs}