diff --git a/tox.ini b/tox.ini
index f86bbde..500517b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,10 +1,9 @@
 [tox]
-envlist = py27,pep8
+envlist = py27,py35,pep8
 minversion = 1.6
 skipsdist = True
 
 [testenv]
-basepython=python2.7
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
@@ -21,12 +20,14 @@ commands =
   {envpython} {toxinidir}/manage.py test apmec_horizon --settings=apmec_horizon.test.settings {posargs}
 
 [testenv:py27]
+basepython=python2.7
 commands =
   {envpython} {toxinidir}/manage.py test apmec_horizon --settings=apmec_horizon.test.settings {posargs}
 
 [tox:jenkins]
 
 [testenv:pep8]
+basepython=python3
 usedevelop = True
 whitelist_externals =
   git
@@ -37,13 +38,16 @@ commands =
   flake8
 
 [testenv:doc]
+basepython=python3
 deps = Sphinx
 commands = sphinx-build doc/source doc/build
 
 [testenv:cover]
+basepython=python3
 setenv = NOSE_WITH_COVERAGE=1
 
 [testenv:venv]
+basepython=python3
 commands = {posargs}
 
 [flake8]
@@ -51,6 +55,7 @@ show-source = True
 max-complexity = 20
 
 [testenv:makemessages]
+basepython=python3
 commands =
     pybabel extract -F babel-django.cfg -o apmec_horizon/locale/django.pot -k gettext_noop -k gettext_lazy -k ngettext_lazy:1,2 -k ugettext_noop -k ugettext_lazy -k ungettext_lazy:1,2 -k npgettext:1c,2,3 -k pgettext_lazy:1c,2 -k npgettext_lazy:1c,2,3 apmec_horizon
     pybabel extract -F babel-djangojs.cfg -o apmec_horizon/locale/djangojs.pot -k gettext_noop -k gettext_lazy -k ngettext_lazy:1,2 -k ugettext_noop -k ugettext_lazy -k ungettext_lazy:1,2 -k npgettext:1c,2,3 -k pgettext_lazy:1c,2 -k npgettext_lazy:1c,2,3 apmec_horizon