diff --git a/cmd-new-session.c b/cmd-new-session.c
index 7f7643bfe..83a027de9 100644
--- a/cmd-new-session.c
+++ b/cmd-new-session.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-new-session.c,v 1.153 2026/10/09 13:12:14 nicm Exp $ */
+/* $OpenBSD: cmd-new-session.c,v 1.154 2026/10/12 07:52:05 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -82,7 +82,8 @@ cmd_new_session_exec(struct cmd *self, struct cmdq_item *item)
 	char			*cause, *cwd = NULL, *cp, *ename;
 	char			*wname = NULL, *sname = NULL, *prefix = NULL;
 	int			 detached, already_attached, is_control = 0;
-	u_int			 sx, sy, dsx, dsy, count = args_count(args);
+	u_int			 sx, sy, dsx, dsy, idx;
+	u_int			 count = args_count(args);
 	struct spawn_context	 sc = { 0 };
 	enum cmd_retval		 retval;
 	struct cmd_find_state    fs;
@@ -316,12 +317,17 @@ cmd_new_session_exec(struct cmd *self, struct cmdq_item *item)
 	 * so add it to the group and synchronize.
 	 */
 	if (group != NULL) {
-		if (sg == NULL) {
-			if (groupwith != NULL) {
-				sg = session_group_new(groupwith->name);
-				session_group_add(sg, groupwith);
-			} else
-				sg = session_group_new(group);
+		if (sg == NULL && groupwith == NULL)
+			sg = session_group_new(group);
+		else if (sg == NULL) {
+			cp = xstrdup(groupwith->name);
+			for (idx = 1; session_group_find(cp) != NULL; idx++) {
+				free(cp);
+				xasprintf(&cp, "%s-%u", groupwith->name, idx);
+			}
+			sg = session_group_new(cp);
+			free(cp);
+			session_group_add(sg, groupwith);
 		}
 		session_group_add(sg, s);
 		session_group_synchronize_to(s);