diff --git a/packages/backend/src/misc/is-reply.ts b/packages/backend/src/misc/is-reply.ts
index 7114a3e0ff..5b5bbbc373 100644
--- a/packages/backend/src/misc/is-reply.ts
+++ b/packages/backend/src/misc/is-reply.ts
@@ -7,5 +7,5 @@ import { MiUser } from '@/models/User.js';
 import { MiNote } from '@/models/Note.js';
 
 export function isReply(note: MiNote, viewerId?: MiUser['id'] | undefined | null): boolean {
-	return note.replyId && note.replyUserId !== note.userId && note.replyUserId !== viewerId;
+	return note.replyId !== undefined && note.replyUserId !== note.userId && note.replyUserId !== viewerId;
 }