diff --git a/tox.ini b/tox.ini
index bc827d5..b0bbb72 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,29 +24,36 @@ commands =
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
 [testenv:common-constraints]
+basepython = python3
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 
 [testenv:pep8]
+basepython = python3
 commands = flake8 . doc/ext
 
 [testenv:pep8-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = {[testenv:pep8]commands}
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:venv-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 commands =
     py.test --cov-config .coveragerc --cov-report html --cov=os_faults "os_faults/tests/unit"
     coverage html -d {envlogdir}
     coverage report
 
 [testenv:cover-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = {[testenv:cover]commands}
 
@@ -71,22 +78,27 @@ deps = {[testenv:integration]deps}
 commands = {[testenv:integration]commands}
 
 [testenv:docs]
+basepython = python3
 commands =
     rm -rf doc/build
     python setup.py build_sphinx --warning-is-error
 
 [testenv:releasenotes]
+basepython = python3
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:docs-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = {[testenv:docs]commands}
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [testenv:debug-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = {[testenv:debug]commands}