diff --git a/tox.ini b/tox.ini
index bf609a747..485816d45 100644
--- a/tox.ini
+++ b/tox.ini
@@ -12,6 +12,8 @@ commands =
 
 setenv =
     PYTHONPATH = {toxinidir}
+    PYTHONHASHSEED = 0
+# https://testrun.org/tox/latest/example/basic.html#special-handling-of-pythonhas
 
 [testenv:cover]
 basepython = python2.7