diff --git a/tox.ini b/tox.ini
index ce0c797..4d5e5ca 100644
--- a/tox.ini
+++ b/tox.ini
@@ -21,6 +21,7 @@ commands =
   charm-build --log-level DEBUG -o {toxinidir}/build .
 
 [testenv:venv]
+basepython = python3
 commands = {posargs}
 
 [testenv:py27]
@@ -48,4 +49,5 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = /bin/true
 
 [testenv:pep8]
+basepython = python3
 commands = /bin/true