diff --git a/doc/source/conf.py b/doc/source/conf.py
index 45ec460945..f6884a5bee 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -144,7 +144,7 @@ openstackdocs_bug_tag = ''
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
-language = None
+language = 'en'
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used: