diff --git a/tox.ini b/tox.ini
index 002ad7cf1..d33bb050d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -16,14 +16,17 @@ passenv=
     DUMP_CONFIG_GRAPH
 
 [testenv:pep8]
+basepython = python3
 commands =
   flake8 {posargs}
   dib-lint
 
 [testenv:pylint]
+basepython = python3
 commands = pylint --rcfile pylint.cfg diskimage_builder
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:func]
@@ -34,12 +37,15 @@ commands = {toxinidir}/tests/run_functests.sh {posargs}
 # NOTE: this is "setup.py test" (*not* testr) which is a pbr wrapper
 # around testr.  This understands --coverage-package-name which we
 # need due to underscore issues.
+basepython = python3
 commands = python setup.py test --coverage --coverage-package-name diskimage_builder --testr-args='{posargs}'
 
 [testenv:docs]
+basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
+basepython = python3
 commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [flake8]