diff --git a/tox.ini b/tox.ini
index 576443c..0e820c4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,9 +11,11 @@ deps = -r{toxinidir}/requirements.txt
 whitelist_externals = find
 
 [testenv:pep8]
+basepython = python3
 commands = flake8
 
 [testenv:venv]
+basepython = python3
 # NOTE(jaegerandi): this target does not use constraints because
 # upstream infra does not yet support it. Once that's fixed, we can
 # drop the install_command.