diff --git a/tox.ini b/tox.ini
index b2e34f8..e0b8b98 100644
--- a/tox.ini
+++ b/tox.ini
@@ -17,20 +17,25 @@ commands = stestr run --slowest {posargs}
 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 {posargs}
 
 [testenv:pep8-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = flake8 {posargs}
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:venv-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = {posargs}
 
 [testenv:cover]
+basepython = python3
 deps = {[testenv]deps}
     coverage
 setenv =
@@ -42,6 +47,7 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:cover-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 deps = {[testenv]deps}
     coverage
@@ -54,16 +60,20 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
+basepython = python3
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:docs-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = python setup.py build_sphinx
 
 [testenv:debug]
+basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [testenv:debug-constraints]
+basepython = python3
 install_command = {[testenv:common-constraints]install_command}
 commands = oslo_debug_helper {posargs}