diff --git a/tox.ini b/tox.ini
index a9072acf62f..98f268829a3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,10 +35,12 @@ deps=
 
 [testenv:du10]
 deps=
+    mock
     docutils==0.10
     {[testenv]deps}
 
 [testenv:du11]
 deps=
+    mock
     docutils==0.11
     {[testenv]deps}