diff --git a/tox.ini b/tox.ini
index 2ff1f7d8e..3e559af66 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,6 +24,7 @@ commands =
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
 [testenv:pep8]
+basepython = python3
 commands =
   doc8 -e .rst doc/source/ CONTRIBUTING.rst HACKING.rst README.rst
   bash tools/flake8wrap.sh {posargs}
@@ -33,11 +34,13 @@ commands =
   bandit -r zun -x tests -n5 -ll --skip B303,B604
 
 [testenv:venv]
+basepython = python3
 #set PYTHONHASHSEED=0 to prevent oslo_policy.sphinxext from randomly failing.
 setenv = PYTHONHASHSEED=0
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --source zun --parallel-mode
@@ -49,12 +52,14 @@ commands =
     coverage report
 
 [testenv:docs]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
     doc8 -e .rst specs/ doc/source/ CONTRIBUTING.rst HACKING.rst README.rst
     sphinx-build -W -d doc/build/doctrees -b html doc/source/ doc/build/html
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [testenv:debug-py27]
@@ -66,6 +71,7 @@ basepython = python3.5
 commands = oslo_debug_helper {posargs}
 
 [testenv:migration]
+basepython = python3
 setenv = {[testenv]setenv}
    OS_TEST_PATH=./zun/tests/migration
 deps = {[testenv]deps}
@@ -87,6 +93,7 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 local-check-factory = zun.hacking.checks.factory
 
 [testenv:fast8]
+basepython = python3
 # NOTE(sheel.rana): `tox -e fast8` cab be used to run pep8 command only for
 # updated code instead for running whole code base.
 # Use same environment directory as pep8 env to save space and install time.
@@ -96,19 +103,23 @@ commands =
   {toxinidir}/tools/fast8.sh
 
 [testenv:releasenotes]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:genconfig]
+basepython = python3
 envdir = {toxworkdir}/venv
 commands =
     oslo-config-generator --config-file etc/zun/zun-config-generator.conf
 
 [testenv:genpolicy]
+basepython = python3
 commands =
     oslopolicy-sample-generator --config-file etc/zun/zun-policy-generator.conf
 
 [testenv:api-ref]
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf api-ref/build