diff --git a/packages/communication/src/discord-provider.ts b/packages/communication/src/discord-provider.ts
index ff6ea21fb..4f442cad0 100644
--- a/packages/communication/src/discord-provider.ts
+++ b/packages/communication/src/discord-provider.ts
@@ -1048,11 +1048,13 @@ export class DiscordCommunicationProvider implements CommunicationProviderAdapte
     guildId: string;
     channelId: string;
   }): Promise<DiscordChannelPermissionDiagnostics> {
-    const [bot, member, roles, channel] = await Promise.all([
-      this.getBotInfo(),
+    // The guild-members endpoint takes a real user id — Discord rejects the
+    // literal `@me` there with 400 Invalid Form Body (unlike /users/@me).
+    const bot = await this.getBotInfo();
+    const [member, roles, channel] = await Promise.all([
       this.request<{ roles?: string[] }>(
         'GET',
-        `/guilds/${input.guildId}/members/@me`,
+        `/guilds/${input.guildId}/members/${bot.id}`,
         undefined,
         { retryNetworkErrors: true, retryServerErrors: true },
       ),
diff --git a/packages/communication/src/mock-discord-server.ts b/packages/communication/src/mock-discord-server.ts
index 18e9e9100..38020be35 100644
--- a/packages/communication/src/mock-discord-server.ts
+++ b/packages/communication/src/mock-discord-server.ts
@@ -409,7 +409,17 @@ export class MockDiscordServer {
         ),
       );
     }
-    if (method === 'GET' && path === `/guilds/${this.guildId}/members/@me`) {
+    const guildMember = /^\/guilds\/([^/]+)\/members\/([^/?]+)$/u.exec(path);
+    if (method === 'GET' && guildMember && guildMember[1] === this.guildId) {
+      // Real Discord rejects the literal `@me` on this route (unlike
+      // /users/@me); keep the mock as strict so provider code cannot pass
+      // against the mock while failing in production.
+      if (guildMember[2] === '@me') {
+        return jsonResponse({ message: 'Invalid Form Body', code: 50035 }, 400);
+      }
+      if (guildMember[2] !== this.bot.id) {
+        return jsonResponse({ message: 'Unknown Member', code: 10007 }, 404);
+      }
       return jsonResponse({ user: this.bot, roles: ['role-roomote'] });
     }
     if (method === 'GET' && path === `/guilds/${this.guildId}/roles`) {