diff --git a/packages/backend/src/core/ReactionService.ts b/packages/backend/src/core/ReactionService.ts
index 64c7b2ed03..843d2e78f5 100644
--- a/packages/backend/src/core/ReactionService.ts
+++ b/packages/backend/src/core/ReactionService.ts
@@ -167,24 +167,12 @@ export class ReactionService {
 			reaction,
 		};
 
-		// Create reaction
 		try {
 			await this.noteReactionsRepository.insert(record);
 		} catch (e) {
 			if (isDuplicateKeyValueError(e)) {
-				const exists = await this.noteReactionsRepository.findOneByOrFail({
-					noteId: note.id,
-					userId: user.id,
-				});
-
-				if (exists.reaction !== reaction) {
-					// 別のリアクションがすでにされていたら置き換える
-					await this.delete(user, note);
-					await this.noteReactionsRepository.insert(record);
-				} else {
-					// 同じリアクションがすでにされていたらエラー
-					throw new IdentifiableError('51c42bb4-931a-456b-bff7-e5a8a70dd298');
-				}
+				// 同じリアクションがすでにされていたらエラー
+				throw new IdentifiableError('51c42bb4-931a-456b-bff7-e5a8a70dd298');
 			} else {
 				throw e;
 			}
@@ -281,11 +269,12 @@ export class ReactionService {
 	}
 
 	@bindThis
-	public async delete(user: { id: MiUser['id']; host: MiUser['host']; isBot: MiUser['isBot']; }, note: MiNote) {
+	public async delete(user: { id: MiUser['id']; host: MiUser['host']; isBot: MiUser['isBot']; }, note: MiNote, _reaction?: string | null) {
 		// if already unreacted
 		const exist = await this.noteReactionsRepository.findOneBy({
 			noteId: note.id,
 			userId: user.id,
+			reaction: _reaction ?? FALLBACK,
 		});
 
 		if (exist == null) {
diff --git a/packages/backend/src/models/NoteReaction.ts b/packages/backend/src/models/NoteReaction.ts
index 42dfcaa9ad..366a4423f7 100644
--- a/packages/backend/src/models/NoteReaction.ts
+++ b/packages/backend/src/models/NoteReaction.ts
@@ -9,7 +9,8 @@ import { MiUser } from './User.js';
 import { MiNote } from './Note.js';
 
 @Entity('note_reaction')
-@Index(['userId', 'noteId'], { unique: true })
+@Index(['userId', 'noteId'])
+@Index(['userId', 'noteId', 'reaction'], { unique: true })
 export class MiNoteReaction {
 	@PrimaryColumn(id())
 	public id: string;