diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index e005a7ff71..797c6267b1 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -80,7 +80,7 @@ export class ApRendererService {
 	}
 
 	@bindThis
-	public renderAnnounce(object: string | IObject | null, note: Note): IAnnounce {
+	public renderAnnounce(object: string | IObject, note: Note): IAnnounce {
 		const attributedTo = this.userEntityService.genLocalUserUri(note.userId);
 
 		let to: string[] = [];
diff --git a/packages/backend/test/unit/activitypub.ts b/packages/backend/test/unit/activitypub.ts
index e378cfeb65..45ad1bf447 100644
--- a/packages/backend/test/unit/activitypub.ts
+++ b/packages/backend/test/unit/activitypub.ts
@@ -248,7 +248,7 @@ describe('ActivityPub', () => {
 
 	describe('Renderer', () => {
 		test('Render an announce with visibility: followers', () => {
-			rendererService.renderAnnounce(null, {
+			rendererService.renderAnnounce('hoge', {
 				createdAt: new Date(0),
 				visibility: 'followers',
 			} as Note);