diff --git a/tox.ini b/tox.ini
index b02203ce..491ccf15 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_*
 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
@@ -72,4 +76,4 @@ commands =
 
 [flake8]
 ignore = E402,E226
-exclude = hooks/charmhelpers
+exclude = */charmhelpers