diff --git a/packages/server/test/federation-identity-deletion.test.ts b/packages/server/test/federation-identity-deletion.test.ts
index 90284367..d3a469c3 100644
--- a/packages/server/test/federation-identity-deletion.test.ts
+++ b/packages/server/test/federation-identity-deletion.test.ts
@@ -20,4 +20,30 @@ describe('Federation identity deletion — server suite', () => {
     expect(harness.remote.origin).toMatch(/^http:\/\/127\.0\.0\.1:\d+$/);
     expect(sharedHmacSecret).toHaveLength(64);
   });
+
+  it('#11 returns 400 for invalid mode', async () => {
+    const { createFederatedUser } = await import('./helpers/testUsers.js');
+    const { homeUser } = await createFederatedUser(harness.home, harness.remote, 't11');
+    const res = await fetch(`${harness.home.origin}/api/users/@me/federation-identity/delete`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${homeUser.token}` },
+      body: JSON.stringify({ origins: [harness.remote.origin], mode: 'foo' }),
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(String(body.error)).toMatch(/Invalid mode/);
+  });
+
+  it('#12 returns 400 for empty origins', async () => {
+    const { createFederatedUser } = await import('./helpers/testUsers.js');
+    const { homeUser } = await createFederatedUser(harness.home, harness.remote, 't12');
+    const res = await fetch(`${harness.home.origin}/api/users/@me/federation-identity/delete`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${homeUser.token}` },
+      body: JSON.stringify({ origins: [], mode: 'full' }),
+    });
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(String(body.error)).toMatch(/origins/);
+  });
 });