diff --git a/tox.ini b/tox.ini
index 1087a1969..704874a9f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -79,6 +79,7 @@ commands =
 setenv =
     {[testenv]setenv}
     CERTBOT_OLDEST=1
+    PIP_FORCE_REINSTALL=1
 
 [testenv:py27-acme-oldest]
 commands =