diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index 5c71dbc62691dfadc2da48da310507eb9cd960ab..9d326e27375e524c7bfbe5df40d08c41f3054e0e 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -398,7 +398,7 @@ export class ApPersonService implements OnModuleInit {
 					alsoKnownAs: person.alsoKnownAs,
 					// We use "!== false" to handle incorrect types, missing / null values, and "default to true" logic.
 					hideOnlineStatus: person.hideOnlineStatus !== false,
-					isExplorable: person.discoverable,
+					isExplorable: person.discoverable !== false,
 					username: person.preferredUsername,
 					approved: true,
 					usernameLower: person.preferredUsername?.toLowerCase(),
@@ -602,7 +602,7 @@ export class ApPersonService implements OnModuleInit {
 			alsoKnownAs: person.alsoKnownAs ?? null,
 			// We use "!== false" to handle incorrect types, missing / null values, and "default to true" logic.
 			hideOnlineStatus: person.hideOnlineStatus !== false,
-			isExplorable: person.discoverable,
+			isExplorable: person.discoverable !== false,
 			...(await this.resolveAvatarAndBanner(exist, person.icon, person.image, person.backgroundUrl).catch(() => ({}))),
 		} as Partial<MiRemoteUser> & Pick<MiRemoteUser, 'isBot' | 'isCat' | 'speakAsCat' | 'isLocked' | 'movedToUri' | 'alsoKnownAs' | 'isExplorable'>;
 
diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index d67f8cf62e50873f55f99acb73a274d990f1179b..119a9d8ccbaee7210381ac95360f6bfaa8524b27 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?: {