diff --git a/.zuul.yaml b/.zuul.yaml
index 60c7788e3..0210d6406 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -41,6 +41,7 @@
         # support HTTPS endpoints now, so tls-proxy needs to be disabled.
         tls-proxy: false
       devstack_localrc:
+        USE_PYTHON3: true
         LIBS_FROM_GIT: python-neutronclient
       devstack_plugins:
         neutron-vpnaas: https://opendev.org/openstack/neutron-vpnaas
diff --git a/tox.ini b/tox.ini
index 13a45d2d2..e248ee06d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -36,6 +36,7 @@ basepython = python3
 commands = {posargs}
 
 [testenv:functional]
+basepython = python3
 setenv =
   OS_TEST_PATH = ./neutronclient/tests/functional
   OS_NEUTRONCLIENT_EXEC_DIR = {envdir}/bin