diff --git a/Manuals/Docbook/repository.docbook b/Manuals/Docbook/repository.docbook
index 8c40a1e..b9373cc 100644
--- a/Manuals/Docbook/repository.docbook
+++ b/Manuals/Docbook/repository.docbook
@@ -24,7 +24,7 @@
 
 ]>
 
-<book lang="en">
+<book lang="en-US">
 
     <bookinfo>