# UNDF: UNDF-2026-000000264
--- a/apps/meteor/app/lib/server/lib/notifyUsersOnMessage.ts
+++ b/apps/meteor/app/lib/server/lib/notifyUsersOnMessage.ts
@@ -125,7 +125,8 @@ async function updateUsersSubscriptions(message: IMessage, room: IRoom): Promis
 	await Promise.all([
 		Subscriptions.setAlertForRoomIdExcludingUserId(message.rid, message.u._id),
 		Subscriptions.setOpenForRoomIdExcludingUserId(message.rid, message.u._id),
 	]);

+	const userIdSet = new Set(userIds);
 	subs.forEach((sub) => {
-		const hasUserMention = userIds.includes(sub.u._id);
+		const hasUserMention = userIdSet.has(sub.u._id);
 		const shouldIncUnread = hasUserMention || toAll || toHere || unreadAllMessages;
 		void notifyOnSubscriptionChanged(