diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index 9abb60ae0e..8f436f343d 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -595,7 +595,7 @@ export class ApRendererService {
 	}
 
 	@bindThis
-	public renderNoteUpdate(object: IObject, note: MiNote, user: { id: MiUser['id'] }): IUpdate {
+	public renderNoteUpdate(object: IPost, note: MiNote, user: { id: MiUser['id'] }): IUpdate {
 		const activity: IUpdate = {
 			id: `${this.config.url}/users/${user.id}#updates/${new Date().getTime()}`,
 			actor: this.userEntityService.genLocalUserUri(note.userId),
diff --git a/packages/backend/test/unit/activitypub.ts b/packages/backend/test/unit/activitypub.ts
index 6962608106..a685dc556d 100644
--- a/packages/backend/test/unit/activitypub.ts
+++ b/packages/backend/test/unit/activitypub.ts
@@ -386,6 +386,25 @@ describe('ActivityPub', () => {
 		});
 	});
 
+	describe('Update', async () => {
+		const actor = createRandomActor();
+
+		const post = {
+			'@context': 'https://www.w3.org/ns/activitystreams',
+			id: `${host}/users/${secureRndstr(8)}`,
+			type: 'Note',
+			attributedTo: actor.id,
+			to: 'https://www.w3.org/ns/activitystreams#Public',
+			content: 'あ',
+		};
+
+		const note = await noteService.createNote(post.id, resolver, true);
+
+		test('Update note', async () => {
+			rendererService.renderNoteUpdate(await rendererService.renderNote(note!, false, true), note!, actor);
+		});
+	});
+
 	describe('JSON-LD', () =>{
 		test('Compaction', async () => {
 			const jsonLd = jsonLdService.use();