diff --git a/tox.ini b/tox.ini
index f6faa08b27..0e5c0b3ce0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -37,6 +37,8 @@ basepython = python3.5
 commands = oslo_debug_helper {posargs}
 
 [testenv:pep8]
+# Let's gate pep8 under py3 by default because the py3 checks are stricter.
+basepython = python3
 commands =
   flake8 {posargs}
   # Run bashate during pep8 runs to ensure violations are caught by
@@ -87,6 +89,8 @@ commands =
   {toxinidir}/tools/cover.sh {posargs}
 
 [testenv:fast8]
+# Let's run fast8 under py3 by default because the py3 checks are stricter.
+basepython = python3
 commands =
   {toxinidir}/tools/fast8.sh