diff --git a/tox.ini b/tox.ini
index c79c5632..e4707570 100644
--- a/tox.ini
+++ b/tox.ini
@@ -12,6 +12,7 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = {posargs}
 
 [testenv:ical]
+basepython = python3
 whitelist_externals = mkdir
 commands =
     mkdir -p output/calendars