diff --git a/tox.ini b/tox.ini
index bfc62fe301..c9ba0f0644 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,7 +4,7 @@ skipsdist = True
 envlist = validate,py27,pep8,pip-install
 
 [testenv]
-basepython = python2.7
+basepython = python3
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
@@ -14,11 +14,13 @@ commands =
   stestr run {posargs}
 
 [testenv:py27-check-uc]
+basepython = python2.7
 install_command = pip install -U {opts} -c {toxinidir}/upper-constraints.txt {packages}
 deps = -r{toxinidir}/upper-constraints.txt
 commands = check-conflicts {toxinidir}/upper-constraints.txt {toxinidir}/upper-constraints-xfails.txt
 
 [testenv:py27-check-lc]
+basepython = python2.7
 install_command = pip install -U {opts} -c {toxinidir}/lower-constraints.txt {packages}
 deps = -r{toxinidir}/lower-constraints.txt
 commands = check-conflicts {toxinidir}/lower-constraints.txt {toxinidir}/lower-constraints-xfails.txt