diff --git a/src/window.h b/src/window.h
index 10aa6338139..ca507cd1625 100644
--- a/src/window.h
+++ b/src/window.h
@@ -126,7 +126,9 @@ struct window
        set up for it in advance.  Set by scrolling commands.  */
     Lisp_Object force_start;
     /* Non-nil means we have explicitly changed the value of start,
-       but that the next redisplay is not obliged to use the new value.  */
+       but that the next redisplay is not obliged to use the new value.
+       This is used in Fdelete_other_windows to force a call to
+       Vwindow_scroll_functions.  */
     Lisp_Object optional_new_start;
     /* Number of columns display within the window is scrolled to the left.  */
     Lisp_Object hscroll;