diff --git a/tmux.h b/tmux.h
index 1691a26fa..54910a617 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1434 2026/09/08 08:33:10 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1435 2026/09/08 08:37:56 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -3700,6 +3700,7 @@ struct window_pane *window_pane_previous_by_number(struct window *,
 			struct window_pane *, u_int);
 int		 window_pane_index(struct window_pane *, u_int *);
 int		 window_pane_zindex(struct window_pane *, u_int *);
+int		 window_pane_last_index(struct window_pane *, u_int *);
 u_int		 window_count_panes(struct window *, int);
 void		 window_destroy_panes(struct window *);
 struct window_pane *window_pane_find_by_id_str(const char *);
diff --git a/window.c b/window.c
index 9feb1e71c..cbe65c615 100644
--- a/window.c
+++ b/window.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: window.c,v 1.373 2026/08/24 21:17:19 nicm Exp $ */
+/* $OpenBSD: window.c,v 1.374 2026/09/08 08:37:56 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1248,6 +1248,21 @@ window_pane_zindex(struct window_pane *wp, u_int *i)
 	return (-1);
 }
 
+int
+window_pane_last_index(struct window_pane *wp, u_int *i)
+{
+	struct window		*w = wp->window;
+	struct window_pane	*wq;
+
+	*i = 0;
+	TAILQ_FOREACH(wq, &w->last_panes, sentry) {
+		if (wq == wp)
+			return (0);
+		(*i)++;
+	}
+	return (-1);
+}
+
 u_int
 window_count_panes(struct window *w, int with_floating)
 {