diff --git a/tox.ini b/tox.ini
index 2e42072ac..d6c1a4aaf 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,6 +13,7 @@ commands =
          trial --rterrors {posargs:allmydata}
 
 [testenv:deprecations]
+basepython=python2.7
 passenv = USERPROFILE HOMEDRIVE HOMEPATH
 setenv =
          PYTHONWARNINGS=default::DeprecationWarnings