diff --git a/CHANGELOG.md b/CHANGELOG.md
index 24b5f6e661..fd8eaf00e8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,6 +30,8 @@
   (Cherry-picked from https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/737)
 - Fix: ロックダウンされた期間指定のノートがStreaming経由でLTLに出現するのを修正 ( #15200 )
 - Fix: disableClustering設定時の初期化ロジックを調整( #15223 )
+- Fix: ActivityPubリクエストかどうかの判定が正しくない問題を修正  
+  (Cherry-picked from https://github.com/MisskeyIO/misskey/pull/869)
 
 ## 2024.11.0
 
diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index f34f6583d3..8c4b13a40a 100644
--- a/packages/backend/src/server/ActivityPubServerService.ts
+++ b/packages/backend/src/server/ActivityPubServerService.ts
@@ -519,8 +519,8 @@ export class ActivityPubServerService {
 			},
 			deriveConstraint(request: IncomingMessage) {
 				const accepted = accepts(request).type(['html', ACTIVITY_JSON, LD_JSON]);
-				const isAp = typeof accepted === 'string' && !accepted.match(/html/);
-				return isAp ? 'ap' : 'html';
+				if (accepted === false) return null;
+				return accepted !== 'html' ? 'ap' : 'html';
 			},
 		});