diff --git a/packages/backend/src/server/api/stream/channels/mahjong-room.ts b/packages/backend/src/server/api/stream/channels/mahjong-room.ts
index 353d0b5ba7..3388b2f16f 100644
--- a/packages/backend/src/server/api/stream/channels/mahjong-room.ts
+++ b/packages/backend/src/server/api/stream/channels/mahjong-room.ts
@@ -56,6 +56,7 @@ class MahjongRoomChannel extends Channel {
 			case 'ready': this.ready(body); break;
 			case 'updateSettings': this.updateSettings(body.key, body.value); break;
 			case 'addAi': this.addAi(); break;
+			case 'leave': this.leaveRoom(); break;
 			case 'confirmNextKyoku': this.confirmNextKyoku(); break;
 			case 'dahai': this.dahai(body.tile, body.riichi); break;
 			case 'tsumoHora': this.tsumoHora(); break;
@@ -98,6 +99,13 @@ class MahjongRoomChannel extends Channel {
 		this.mahjongService.addAi(this.roomId!, this.user);
 	}
 
+	@bindThis
+	private async leaveRoom() {
+		if (this.user == null) return;
+
+		this.mahjongService.leaveRoom(this.roomId!, this.user);
+	}
+
 	@bindThis
 	private async dahai(tile: number, riichi = false) {
 		if (this.user == null) return;
diff --git a/packages/misskey-js/src/streaming.types.ts b/packages/misskey-js/src/streaming.types.ts
index 102ad24b24..31ae1b0bce 100644
--- a/packages/misskey-js/src/streaming.types.ts
+++ b/packages/misskey-js/src/streaming.types.ts
@@ -358,6 +358,7 @@ export type Channels = {
 				body: unknown;
 			};
 			addAi: Record<string, never>;
+			leave: Record<string, never>;
 			confirmNextKyoku: Record<string, never>;
 			dahai: {
 				tile: number;