diff --git a/Documentation/conf.py b/Documentation/conf.py
index ed2b43ec7754..f47c3f1682db 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -176,7 +176,7 @@ finally:
 #
 # 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'
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used: