diff --git a/tox.ini b/tox.ini
index b73c644..491ccf1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,3 +1,6 @@
+# Classic charm: ./tox.ini
+# This file is managed centrally by release-tools and should not be modified
+# within individual charm repos.
 [tox]
 envlist = pep8,py27
 skipsdist = True
@@ -6,10 +9,11 @@ skipsdist = True
 setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
          AMULET_SETUP_TIMEOUT=2700
-passenv = HOME TERM AMULET_HTTP_PROXY AMULET_OS_VIP
 install_command =
   pip install --allow-unverified python-apt {opts} {packages}
 commands = ostestr {posargs}
+whitelist_externals = juju
+passenv = HOME TERM AMULET_*
 
 [testenv:py27]
 basepython = python2.7
@@ -20,7 +24,7 @@ deps = -r{toxinidir}/requirements.txt
 basepython = python2.7
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = flake8 {posargs} --exclude */charmhelpers hooks unit_tests tests actions
+commands = flake8 {posargs} hooks unit_tests tests actions
            charm-proof
 
 [testenv:venv]
@@ -72,4 +76,4 @@ commands =
 
 [flake8]
 ignore = E402,E226
-exclude = hooks/charmhelpers
+exclude = */charmhelpers