diff --git a/packages/backend/src/remote/resolve-user.ts b/packages/backend/src/remote/resolve-user.ts
index 8122a7626..68f4d2d90 100644
--- a/packages/backend/src/remote/resolve-user.ts
+++ b/packages/backend/src/remote/resolve-user.ts
@@ -207,12 +207,13 @@ export function getMentionFallbackUri(username: string, host: string | null, obj
 	return fallback;
 }
 
-export async function resolveMentionWithFallback(username: string, host: string | null, objectHost: string | null, cache: IMentionedRemoteUsers): Promise<string> {
+export async function resolveMentionWithFallback(username: string, host: string | null, objectHost: string | null, cache: IMentionedRemoteUsers, cachedOnly: boolean = false): Promise<string> {
 	const fallback = getMentionFallbackUri(username, host, objectHost);
 
 	const cached = cache.find(r => r.username.toLowerCase() === username.toLowerCase() && r.host === host);
 	if (cached) return cached.url ?? cached.uri ?? fallback;
 	if ((host === null && objectHost === null) || host === config.domain) return fallback;
+	if (cachedOnly) return fallback;
 
 	return mentionUriCache.fetch(fallback, async () => {
 		try {
diff --git a/packages/backend/src/server/api/mastodon/helpers/mfm.ts b/packages/backend/src/server/api/mastodon/helpers/mfm.ts
index 39c20e5d4..8326a4b53 100644
--- a/packages/backend/src/server/api/mastodon/helpers/mfm.ts
+++ b/packages/backend/src/server/api/mastodon/helpers/mfm.ts
@@ -136,18 +136,27 @@ export class MfmHelpers {
             },
 
             async mention(node) {
-                const el = doc.createElement("span");
-                el.setAttribute("class", "h-card");
-                el.setAttribute("translate", "no");
-                const a = doc.createElement("a");
                 const { username, host, acct } = node.props;
-                a.href = await resolveMentionWithFallback(username, host, objectHost, mentionedRemoteUsers);
-                a.className = "u-url mention";
-                const span = doc.createElement("span");
-                span.textContent = username;
-                a.textContent = '@';
-                a.appendChild(span);
-                el.appendChild(a);
+                const fallback = await resolveMentionWithFallback(username, host, objectHost, mentionedRemoteUsers, true);
+                const isLocal = (host === null && objectHost === null) || host === config.domain;
+                const isInvalid = fallback.startsWith(config.url) && !isLocal;
+
+                const el = doc.createElement("span");
+                if (isInvalid) {
+                    el.textContent = acct;
+                } else {
+                    el.setAttribute("class", "h-card");
+                    el.setAttribute("translate", "no");
+                    const a = doc.createElement("a");
+                    a.href = fallback;
+                    a.className = "u-url mention";
+                    const span = doc.createElement("span");
+                    span.textContent = username;
+                    a.textContent = '@';
+                    a.appendChild(span);
+                    el.appendChild(a);
+                }
+
                 return el;
             },