diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 7d24642146d..03c511cf68c 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -238,6 +238,8 @@
 	     (scroll-step windows integer)
 	     (scroll-conservatively windows integer)
 	     (scroll-margin windows integer)
+	     (automatic-hscroll-margin windows integer "21.3")
+	     (automatic-hscroll-step windows number "21.3")
 	     (truncate-partial-width-windows display boolean)
 	     (mode-line-inverse-video modeline boolean)
 	     (mode-line-in-non-selected-windows modeline boolean "21.3")