diff --git a/tox.ini b/tox.ini
index 7e1c4ff..227acc3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,6 +4,7 @@ distribute = False
 envlist = py35,py27,pep8
 
 [testenv]
+basepython = python3
 install_command = pip install {opts} {packages}
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
@@ -13,6 +14,9 @@ commands =
   python setup.py test --coverage --coverage-package-name=oslo_config --slowest --testr-args='{posargs}'
   coverage report --show-missing
 
+[testenv:py27]
+basepython = python2.7
+
 [testenv:pep8]
 commands = flake8 {posargs}