diff --git a/Manuals/Userguide/repository.docbook b/Manuals/Userguide/repository.docbook
index aa0ee90..b540018 100644
--- a/Manuals/Userguide/repository.docbook
+++ b/Manuals/Userguide/repository.docbook
@@ -18,7 +18,7 @@
 %Licenses.ent;
 ]>
 
-<book lang="en">
+<book lang="en_US">
 
     <!-- Front matter -->
     <title>The CentOS Artwork Repository</title>