diff --git a/tox.ini b/tox.ini
index 37c0d1c..35b571d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -12,14 +12,18 @@ setenv =
 deps = -r{toxinidir}/test-requirements.txt
 
 [testenv:pep8]
+basepython = python3
 commands = doc8 doc/source README.rst CONTRIBUTING.rst
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:docs]
+basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
+basepython = python3
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html