diff --git a/tox.ini b/tox.ini
index f1dd4f6354..12b42c2b45 100644
--- a/tox.ini
+++ b/tox.ini
@@ -27,6 +27,7 @@ commands =
   venv: {posargs}
 
 [testenv:py35]
+basepython = python3
 setenv =
   PYTHONUNBUFFERED = 1
   {[testenv]setenv}
@@ -58,6 +59,7 @@ commands =
   doc8 doc/source releasenotes/source releasenotes/notes
 
 [testenv:cover]
+basepython = python3
 commands =
   coverage erase
   coverage run {toxinidir}/manage.py test horizon --settings=horizon.test.settings {posargs}
@@ -67,6 +69,7 @@ commands =
   coverage html
 
 [testenv:selenium]
+basepython = python3
 setenv =
   {[testenv]setenv}
   WITH_SELENIUM=1
@@ -74,6 +77,7 @@ setenv =
 commands = {[unit_tests]commands}
 
 [testenv:selenium-headless]
+basepython = python3
 setenv =
   {[testenv]setenv}
   SELENIUM_HEADLESS=1
@@ -82,6 +86,7 @@ setenv =
 commands = {[unit_tests]commands}
 
 [testenv:selenium-phantomjs]
+basepython = python3
 setenv =
   {[testenv]setenv}
   SELENIUM_PHANTOMJS=1
@@ -102,6 +107,7 @@ basepython = python2.7
 commands = nosetests openstack_dashboard.test.integration_tests {posargs}
 
 [testenv:npm]
+basepython = python3
 passenv =
   HOME
   DISPLAY
@@ -111,6 +117,7 @@ commands =
   npm run {posargs:test}
 
 [testenv:tests_system_packages]
+basepython = python3
 # Provide an environment for system packagers that dont want anything from pip
 # Any extra deps needed for this env can be passed by setting TOX_EXTRA_DEPS
 sitepackages = True
@@ -122,6 +129,7 @@ commands =
   {[unit_tests]commands}
 
 [testenv:docs]
+basepython = python3
 # We need to install horizon dependecies to build module references
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
@@ -131,6 +139,7 @@ commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
+basepython = python3
 # There is no need to install horizon.
 usedevelop = False
 deps =
@@ -140,6 +149,7 @@ commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:manage]
+basepython = python3
 # we don't need to install test-requirements.txt
 # modules in requirements.txt are installed due to usedevelop=True
 # so 'deps' can be empty.