diff --git a/tox.ini b/tox.ini
index 4df7c03ffccc661d80f85ca3762979392b9f4aa0..d5a55579949863c8a79de03793a7e3b995088f33 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,8 +8,8 @@ commands={envbindir}/unit2 discover []
 [testenv:py26]
 commands=
     {envbindir}/unit2 discover []
-    {envbindir}/sphinx-build -b doctest docs html
-    {envbindir}/sphinx-build docs html
+    {envbindir}/sphinx-build -E -b doctest docs html
+    {envbindir}/sphinx-build -E docs html
 deps =
     unittest2
     sphinx
@@ -17,7 +17,7 @@ deps =
 [testenv:py27]
 commands=
     {envbindir}/unit2 discover []
-    {envbindir}/sphinx-build -b doctest docs html
+    {envbindir}/sphinx-build -E -b doctest docs html
 deps =
     unittest2
     sphinx