diff --git a/tox.ini b/tox.ini
index faccbdb..944ef85 100644
--- a/tox.ini
+++ b/tox.ini
@@ -30,6 +30,7 @@
     python setup.py check --restructuredtext --strict
 
 [testenv:docs-linkcheck]
+extras =
 deps =
     sphinx
 basepython = python2.7