diff --git a/tox.ini b/tox.ini
index 5be01f3f..c478a7b6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,6 @@
 [tox]
 skipsdist = True
+minversion = 2.3.1
 envlist = py35, pep8, cover, bandit
 
 [testenv]
@@ -19,12 +20,14 @@ commands =
     rm -Rf .testrepository/times.dbm
 
 [testenv:py35]
+basepython = python3.5
 commands =
     {[testenv]commands}
     stestr run {posargs}
     stestr slowest
 
 [testenv:py36]
+basepython = python3.6
 commands =
     {[testenv]commands}
     stestr run {posargs}