diff --git a/packages/backend/src/server/api/mastodon/converters/note.ts b/packages/backend/src/server/api/mastodon/converters/note.ts
index 7ef55fc06..a592529cf 100644
--- a/packages/backend/src/server/api/mastodon/converters/note.ts
+++ b/packages/backend/src/server/api/mastodon/converters/note.ts
@@ -88,7 +88,7 @@ export class NoteConverter {
 
 				const isPinned = user && note.userId === user.id
 					? UserNotePinings.exist({ where: {userId: user.id, noteId: note.id } })
-					: false;
+					: undefined;
 
         // noinspection ES6MissingAwait
 				return await awaitAll({
diff --git a/packages/backend/src/server/api/mastodon/entities/status.ts b/packages/backend/src/server/api/mastodon/entities/status.ts
index 76132eaf8..db476b1a5 100644
--- a/packages/backend/src/server/api/mastodon/entities/status.ts
+++ b/packages/backend/src/server/api/mastodon/entities/status.ts
@@ -37,7 +37,7 @@ namespace MastodonEntity {
 		poll: Poll | null;
 		application: Application | null;
 		language: string | null;
-		pinned: boolean | null;
+		pinned: boolean | undefined;
 		reactions: Array<Reaction>;
 		quote: Status | null;
 		bookmarked: boolean;