diff --git a/src/misc/is-duplicate-key-value-error.ts b/src/misc/is-duplicate-key-value-error.ts
index 23d8ceb1b7..f5343d187c 100644
--- a/src/misc/is-duplicate-key-value-error.ts
+++ b/src/misc/is-duplicate-key-value-error.ts
@@ -1,3 +1,5 @@
-export function isDuplicateKeyValueError(e: Error): boolean {
-	return e.message.startsWith('duplicate key value');
+import { QueryFailedError } from 'typeorm';
+
+export function isDuplicateKeyValueError(e: unknown | Error): boolean {
+	return e instanceof QueryFailedError && e.driverError.code === '23505';
 }
diff --git a/src/models/entities/note-reaction.ts b/src/models/entities/note-reaction.ts
index ed38450bb2..8da79547d6 100644
--- a/src/models/entities/note-reaction.ts
+++ b/src/models/entities/note-reaction.ts
@@ -23,7 +23,7 @@ export class NoteReaction {
 		onDelete: 'CASCADE'
 	})
 	@JoinColumn()
-	public user: User | null;
+	public user?: User | null;
 
 	@Index()
 	@Column(id())
@@ -33,7 +33,7 @@ export class NoteReaction {
 		onDelete: 'CASCADE'
 	})
 	@JoinColumn()
-	public note: Note | null;
+	public note?: Note | null;
 
 	@Column('varchar', {
 		length: 260
diff --git a/src/remote/activitypub/kernel/like.ts b/src/remote/activitypub/kernel/like.ts
index a6f02a1f8f..ce92907e3a 100644
--- a/src/remote/activitypub/kernel/like.ts
+++ b/src/remote/activitypub/kernel/like.ts
@@ -11,6 +11,13 @@ export default async (actor: IRemoteUser, activity: ILike) => {
 
 	await extractEmojis(activity.tag || [], actor.host).catch(() => null);
 
-	await create(actor, note, activity._misskey_reaction || activity.content || activity.name);
+	await create(actor, note, activity._misskey_reaction || activity.content || activity.name).catch(e => {
+		if (e.id === '51c42bb4-931a-456b-bff7-e5a8a70dd298') {
+			return 'skip: already reacted';
+		} else {
+			throw e;
+		}
+	});
+
 	return `ok`;
 };
diff --git a/src/services/note/reaction/create.ts b/src/services/note/reaction/create.ts
index 67e39c4f50..747c6c114c 100644
--- a/src/services/note/reaction/create.ts
+++ b/src/services/note/reaction/create.ts
@@ -12,33 +12,44 @@ import { perUserReactionsChart } from '../../chart';
 import { genId } from '../../../misc/gen-id';
 import { createNotification } from '../../create-notification';
 import deleteReaction from './delete';
+import { NoteReaction } from '../../../models/entities/note-reaction';
+import { isDuplicateKeyValueError } from '../../../misc/is-duplicate-key-value-error';
+import { IdentifiableError } from '../../../misc/identifiable-error';
 
 export default async (user: User, note: Note, reaction?: string) => {
 	reaction = await toDbReaction(reaction, user.host);
 
-	const exist = await NoteReactions.findOne({
+	const inserted: NoteReaction = {
+		id: genId(),
+		createdAt: new Date(),
 		noteId: note.id,
 		userId: user.id,
-	});
+		reaction,
+	};
+
+	// Create reaction
+	try {
+		await NoteReactions.insert(inserted);
+	} catch (e) {
+		if (isDuplicateKeyValueError(e)) {
+			const exists = await NoteReactions.findOneOrFail({
+				noteId: note.id,
+				userId: user.id,
+			});
 
-	if (exist) {
-		if (exist.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 deleteReaction(user, note);
+			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 deleteReaction(user, note);
+				await NoteReactions.insert(inserted);
+			} 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');
+			}
 		} else {
-			// 同じリアクションがすでにされていたら何もしない
-			return;
+			throw e;
 		}
 	}
 
-	// Create reaction
-	const inserted = await NoteReactions.save({
-		id: genId(),
-		createdAt: new Date(),
-		noteId: note.id,
-		userId: user.id,
-		reaction
-	});
 
 	// Increment reactions count
 	const sql = `jsonb_set("reactions", '{${reaction}}', (COALESCE("reactions"->>'${reaction}', '0')::int + 1)::text::jsonb)`;