diff --git a/tox.ini b/tox.ini
index 7e88d1a833f3..34e6a896eead 100644
--- a/tox.ini
+++ b/tox.ini
@@ -45,6 +45,8 @@ commands =
   env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
 
 [testenv:pep8]
+# Let's gate pep8 under py3 by default because the py3 checks are stricter.
+basepython = python3
 deps = {[testenv]deps}
 commands =
   bash tools/flake8wrap.sh {posargs}
@@ -54,6 +56,8 @@ commands =
   bash -c '! find doc/ -type f -name *.json | xargs -t -n1 python -m json.tool 2>&1 > /dev/null | grep -B1 -v ^python'
 
 [testenv:fast8]
+# Let's run fast8 under py3 by default because the py3 checks are stricter.
+basepython = python3
 # This is a subset of the full pep8 check which
 # only runs flake8 on the changes made since
 # HEAD-1. For a full flake8 run including checking