diff --git a/tox.ini b/tox.ini
index 578f23708..08e826f50 100644
--- a/tox.ini
+++ b/tox.ini
@@ -44,7 +44,8 @@ envdir = {toxinidir}/.venv
 usedevelop = true
 
 [testenv:unittests-frozen]
-basepython = python3
+# cx_Freeze doesn't support Python 3.5 yet
+basepython = python3.4
 passenv = {[testenv]passenv}
 skip_install = true
 deps =