diff --git a/tox.ini b/tox.ini
index 5df192e..3fb5307 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,10 @@
 [tox]
 skipsdist = True
 envlist = pep8,py37
-skip_missing_interpreters = True
+# NOTE(beisner): Avoid build/test env pollution by not enabling sitepackages.
+sitepackages = False
+# NOTE(beisner): Avoid false positives by not skipping missing interpreters.
+skip_missing_interpreters = False
 
 [testenv]
 setenv = VIRTUAL_ENV={envdir}