diff --git a/tox.ini b/tox.ini
index 91c6d664..82c1588e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -3,3 +3,6 @@ envlist=py25,py26,py27,pypy
 
 [testenv]
 commands=python run-tests.py
+
+[testenv:py25]
+deps=simplejson