diff --git a/packages/backend/src/core/activitypub/models/ApMentionService.ts b/packages/backend/src/core/activitypub/models/ApMentionService.ts
index 9beefc8fcb..62ae3cf93d 100644
--- a/packages/backend/src/core/activitypub/models/ApMentionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApMentionService.ts
@@ -22,8 +22,8 @@ export class ApMentionService {
 	}
 
 	@bindThis
-	public async extractApMentions(tags: IObject | IObject[] | null | undefined, resolver: Resolver) {
-		const hrefs = unique(this.extractApMentionObjects(tags).map(x => x.href as string));
+	public async extractApMentions(tags: IObject | IObject[] | null | undefined, resolver: Resolver): Promise<User[]> {
+		const hrefs = unique(this.extractApMentionObjects(tags).map(x => x.href));
 
 		const limit = promiseLimit<User | null>(2);
 		const mentionedUsers = (await Promise.all(