diff --git a/bookshop/srv/cat-service.cds b/bookshop/srv/cat-service.cds
index b596cbea..be4f3515 100644
--- a/bookshop/srv/cat-service.cds
+++ b/bookshop/srv/cat-service.cds
@@ -6,5 +6,5 @@ service CatalogService @(path:'/browse') {
   } excluding { createdBy, modifiedBy };
 
   @requires_: 'authenticated-user'
-  action submitOrder (book : Books.ID, amount: Integer);
+  action submitOrder (book : type of Books:ID, amount: Integer);
 }