diff --git a/apps/api/src/routes/setup.ts b/apps/api/src/routes/setup.ts
index d8bae72..63bc98d 100644
--- a/apps/api/src/routes/setup.ts
+++ b/apps/api/src/routes/setup.ts
@@ -27,9 +27,9 @@ import { Hono } from 'hono';
 import type { Context } from 'hono';
 import { zValidator } from '@hono/zod-validator';
 import { z } from 'zod';
-import { eq, sql } from 'drizzle-orm';
+import { eq, sql, and, isNull } from 'drizzle-orm';
 import { db } from '../db/client.js';
-import { users, appConfig } from '../db/schema.js';
+import { users, appConfig, memberCredentials } from '../db/schema.js';
 import { isSetupLocked } from '../lib/setupGuard.js';
 import { COLOR_PALETTE } from '../auth/user.js';
 import {
@@ -352,6 +352,21 @@ setupRouter.post('/complete', async (c) => {
   const locked = await isSetupLocked();
   if (locked) return c.json({ error: 'Setup already complete' }, 423);
 
+  // IN-02: Guard against skipping the credential step — require an unclaimed user
+  // with an associated credential before locking setup. Without this check an operator
+  // could call /complete directly, producing a state where setup_complete=true but no
+  // admin user exists: first OIDC login creates a non-admin with no credential.
+  const [unclaimedWithCred] = await db
+    .select({ id: users.id })
+    .from(users)
+    .innerJoin(memberCredentials, eq(memberCredentials.userId, users.id))
+    .where(and(isNull(users.oidcIss), eq(users.claimed, false)))
+    .limit(1);
+
+  if (!unclaimedWithCred) {
+    return c.json({ error: 'Cannot lock setup: no credential configured' }, 422);
+  }
+
   await db
     .insert(appConfig)
     .values({ key: 'setup_complete', value: 'true' })
diff --git a/apps/api/tests/routes/setup.test.ts b/apps/api/tests/routes/setup.test.ts
index a1fc093..bce06f1 100644
--- a/apps/api/tests/routes/setup.test.ts
+++ b/apps/api/tests/routes/setup.test.ts
@@ -471,14 +471,31 @@ describe('POST /api/setup/credential', () => {
 
 describe('POST /api/setup/complete — 423 guard (SETUP-04 / Pitfall 8)', () => {
   it('returns 200 on first call (fresh setup, wizard not yet locked)', async () => {
+    // IN-02: /complete now requires an unclaimed user + credential before locking.
+    const userId = await seedLocalUser('complete-200');
+    await seedCredential(userId);
+
     const app = await getApp();
     const res = await app.fetch(jsonRequest('POST', '/api/setup/complete'));
     expect(res.status).toBe(200);
   });
 
+  it('returns 422 when /complete is called with no credential configured (IN-02 guard)', async () => {
+    // No unclaimed user or credential — /complete must refuse to lock setup.
+    const app = await getApp();
+    const res = await app.fetch(jsonRequest('POST', '/api/setup/complete'));
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as { error: string };
+    expect(body.error).toMatch(/credential/i);
+  });
+
   // This test is the load-bearing RED test — the 423 must be verified.
   // Second call must return 423 because setup_complete is set after first call.
   it('returns 423 on second call — setup already complete, wizard locked (Pitfall 8)', async () => {
+    // Seed prerequisite so first /complete call succeeds (IN-02 guard).
+    const userId = await seedLocalUser('complete-423');
+    await seedCredential(userId);
+
     const app = await getApp();
 
     // First call — should succeed and set setup_complete