diff --git a/tox.ini b/tox.ini
index 87f4b94..823e625 100644
--- a/tox.ini
+++ b/tox.ini
@@ -3,6 +3,7 @@ minversion = 2.0
 envlist = py35,py27,pep8
 
 [testenv]
+basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     BRANCH_NAME=master
@@ -42,6 +43,7 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 commands = python setup.py build_sphinx
 
 [testenv:py27]
+basepython = python2.7
 commands =
     python setup.py testr --slowest --testr-args='{posargs}'
     sphinx-build -b doctest doc/source doc/build
@@ -57,7 +59,6 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt