diff --git a/packages/backend/src/core/activitypub/ApMfmService.ts b/packages/backend/src/core/activitypub/ApMfmService.ts
index 60868627a..c45c27f86 100644
--- a/packages/backend/src/core/activitypub/ApMfmService.ts
+++ b/packages/backend/src/core/activitypub/ApMfmService.ts
@@ -27,6 +27,6 @@ export class ApMfmService {
 	@bindThis
 	public getNoteHtml(note: MiNote): string | null {
 		if (!note.text) return '';
-		return this.mfmService.toHtml(mfm.parse(note.text), JSON.parse(note.mentionedRemoteUsers));
+		return this.mfmService.toHtml(mfm.parse(note.text), note.mentionedRemoteUsers ? JSON.parse(note.mentionedRemoteUsers) : []);
 	}
 }
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index 7a9d2e21d..b772f3efd 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -353,7 +353,7 @@ export class ApRendererService {
 
 		const attributedTo = this.userEntityService.genLocalUserUri(note.userId);
 
-		const mentions = (JSON.parse(note.mentionedRemoteUsers) as IMentionedRemoteUsers).map(x => x.uri);
+		const mentions = note.mentionedRemoteUsers ? (JSON.parse(note.mentionedRemoteUsers) as IMentionedRemoteUsers).map(x => x.uri) : [];
 
 		let to: string[] = [];
 		let cc: string[] = [];
@@ -371,7 +371,7 @@ export class ApRendererService {
 			to = mentions;
 		}
 
-		const mentionedUsers = note.mentions.length > 0 ? await this.usersRepository.findBy({
+		const mentionedUsers = note.mentions && note.mentions.length > 0 ? await this.usersRepository.findBy({
 			id: In(note.mentions),
 		}) : [];