diff --git a/packages/backend/src/remote/resolve-user.ts b/packages/backend/src/remote/resolve-user.ts
index 442bd5b7b..b1cb5ca13 100644
--- a/packages/backend/src/remote/resolve-user.ts
+++ b/packages/backend/src/remote/resolve-user.ts
@@ -13,6 +13,7 @@ import { IMentionedRemoteUsers } from "@/models/entities/note.js";
 
 const logger = remoteLogger.createSubLogger("resolve-user");
 const uriHostCache = new Cache<string>("resolveUserUriHost", 60 * 60 * 24);
+const mentionUriCache = new Cache<string>("resolveMentionUserUri", 60 * 60 * 72);
 
 export async function resolveUser(
 	username: string,
@@ -188,14 +189,16 @@ export async function resolveMentionWithFallback(username: string, host: string
 	if (cached) return cached.url ?? cached.uri;
 	if ((host === null && objectHost === null) || host === config.domain) return fallback;
 
-	try {
-		const user = await resolveUser(username, host ?? objectHost, false);
-		const profile = await UserProfiles.findOneBy({ userId: user.id });
-		return profile?.url ?? user.uri ?? fallback;
-	}
-	catch {
-		return fallback;
-	}
+	return mentionUriCache.fetch(fallback, async () => {
+		try {
+			const user = await resolveUser(username, host ?? objectHost, false);
+			const profile = await UserProfiles.findOneBy({ userId: user.id });
+			return profile?.url ?? user.uri ?? fallback;
+		}
+		catch {
+			return fallback;
+		}
+	});
 }
 
 export async function getSubjectHostFromUri(uri: string): Promise<string | null> {