diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index edd1041062..b5a97d34c4 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -426,6 +426,9 @@ export class ApInboxService {
 					return 'skip: host in actor.uri !== note.id';
 				}
 			}
+			else {
+				return 'skip: note.id is not a string'
+			}
 		}
 
 		const unlock = await this.appLockService.getApLock(uri);