diff --git a/doc/user/conf.py.in b/doc/user/conf.py.in
index 6059bc9a..6967a9b6 100644
--- a/doc/user/conf.py.in
+++ b/doc/user/conf.py.in
@@ -62,7 +62,7 @@ master_doc = 'index'
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = 'en'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.