diff --git a/tox.ini b/tox.ini
index 157f602c..d4e2a036 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,8 +1,10 @@
 [tox]
-minversion = 2.0
+minversion = 3.1
 envlist = py27,py37,pypy,pep8
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 whitelist_externals =
   find
 deps =
@@ -13,17 +15,18 @@ commands =
   stestr run --slowest {posargs}
 
 [testenv:py27-functional-etcd3gw]
+basepython = python2.7
 commands =
   find . -type f -name "*.pyc" -delete
   {toxinidir}/tools/setup-etcd-env.sh pifpaf -e OSLO_CACHE_TEST run etcd --  stestr run --slowest functional.*
 
 [testenv:py35-functional-etcd3gw]
+basepython = python3.5
 commands =
   find . -type f -name "*.pyc" -delete
   {toxinidir}/tools/setup-etcd-env.sh pifpaf -e OSLO_CACHE_TEST run etcd --  stestr run --slowest functional.*
 
 [testenv:pep8]
-basepython = python3
 deps =
   -r{toxinidir}/test-requirements.txt
 commands =
@@ -32,11 +35,9 @@ commands =
   bandit -r oslo_cache -x tests -n5
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 whitelist_externals = rm
 deps =
   {[testenv]deps}
@@ -46,7 +47,6 @@ commands =
   sphinx-build --keep-going -b html doc/source doc/build/html
 
 [testenv:cover]
-basepython = python3
 setenv =
   PYTHON=coverage run --source oslo_cache --parallel-mode
 commands =
@@ -65,7 +65,6 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 import_exceptions =
 
 [testenv:releasenotes]
-basepython = python3
 whitelist_externals =
   rm
 deps = -r{toxinidir}/doc/requirements.txt
@@ -74,7 +73,6 @@ commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt