diff --git a/tox.ini b/tox.ini
index d40a70799..b3f53cce2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,8 @@ envlist =
 
 [testenv]
 commands = ./runtests.py --fast
+setenv =
+       PYTHONDONTWRITEBYTECODE=1
 
 [testenv:flake8]
 basepython = python2.7