diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index d67f8cf62e..119a9d8ccb 100644
--- a/packages/backend/src/core/activitypub/type.ts
+++ b/packages/backend/src/core/activitypub/type.ts
@@ -202,7 +202,7 @@ export interface IActor extends IObject {
 	manuallyApprovesFollowers?: boolean;
 	movedTo?: string;
 	alsoKnownAs?: string[];
-	discoverable?: boolean;
+	discoverable?: boolean | null;
 	inbox: string;
 	sharedInbox?: string;	// 後方互換性のため
 	publicKey?: {