diff --git a/CHANGELOG.md b/CHANGELOG.md
index 39ce36d678f8..5fa756c0f050 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -67,6 +67,8 @@
 - Fix: User Webhookテスト機能のMock Payloadを修正  
 - Fix: アカウント削除のモデレーションログが動作していないのを修正 (#14996)  
 - Fix: リノートミュートが新規投稿通知に対して作用していなかった問題を修正
+- Fix: Inboxの処理で生じるエラーを誤ってActivityとして処理することがある問題を修正  
+  (Cherry-picked from https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/730)
 - Fix: セキュリティに関する修正
 
 ### Misskey.js
diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index ee3f691c5121..21c7adf7b269 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -28,6 +28,7 @@ import { bindThis } from '@/decorators.js';
 import type { MiRemoteUser } from '@/models/User.js';
 import { GlobalEventService } from '@/core/GlobalEventService.js';
 import { AbuseReportService } from '@/core/AbuseReportService.js';
+import { IdentifiableError } from '@/misc/identifiable-error.js';
 import { getApHrefNullable, getApId, getApIds, getApType, isAccept, isActor, isAdd, isAnnounce, isBlock, isCollection, isCollectionOrOrderedCollection, isCreate, isDelete, isFlag, isFollow, isLike, isMove, isPost, isReject, isRemove, isTombstone, isUndo, isUpdate, validActor, validPost } from './type.js';
 import { ApNoteService } from './models/ApNoteService.js';
 import { ApLoggerService } from './ApLoggerService.js';
@@ -201,13 +202,16 @@ export class ApInboxService {
 
 		await this.apNoteService.extractEmojis(activity.tag ?? [], actor.host).catch(() => null);
 
-		return await this.reactionService.create(actor, note, activity._misskey_reaction ?? activity.content ?? activity.name).catch(err => {
-			if (err.id === '51c42bb4-931a-456b-bff7-e5a8a70dd298') {
+		try {
+			await this.reactionService.create(actor, note, activity._misskey_reaction ?? activity.content ?? activity.name);
+			return 'ok';
+		} catch (err) {
+			if (err instanceof IdentifiableError && err.id === '51c42bb4-931a-456b-bff7-e5a8a70dd298') {
 				return 'skip: already reacted';
 			} else {
 				throw err;
 			}
-		}).then(() => 'ok');
+		}
 	}
 
 	@bindThis
@@ -288,7 +292,7 @@ export class ApInboxService {
 
 		const target = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
-			return e;
+			throw e;
 		});
 
 		if (isPost(target)) return await this.announceNote(actor, activity, target);
@@ -649,7 +653,7 @@ export class ApInboxService {
 
 		const object = await resolver.resolve(activity.object).catch(e => {
 			this.logger.error(`Resolution failed: ${e}`);
-			return e;
+			throw e;
 		});
 
 		// don't queue because the sender may attempt again when timeout