diff --git a/SECURITY.md b/SECURITY.md
index ce0199d..e4cf57e 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -18,10 +18,10 @@ Pinned by `integration/better-auth.test.ts`: `email policy: secret-keyed codes,
 
 - **FAIL IF** a state-changing POST is accepted without an exact `Origin` match, a signature-verified CSRF cookie, a matching `X-CSRF-Token` and an `application/json` body; inspect `protectAuth` in `better-auth-security.ts`.
 - **FAIL IF** an upstream Better Auth route outside the read/write allowlist answers with anything but 404, or a provider callback accepts a method other than GET and Apple's `form_post` relay; inspect `protectAuth`.
-- **FAIL IF** a response leaves without `Cache-Control: no-store`, `Referrer-Policy: no-referrer`, `X-Content-Type-Options: nosniff`, `X-Frame-Options: DENY` and a CSP denying framing, inline script and third-party sources; inspect `protectAuth`.
+- **FAIL IF** a response, including a Workers setup or teardown failure, leaves without `Cache-Control: no-store`, `Referrer-Policy: no-referrer`, `X-Content-Type-Options: nosniff`, `X-Frame-Options: DENY` and a CSP denying framing, inline script and third-party sources; inspect `authSecurityHeaders`, `protectAuth` and `createBetterAuthWorker`.
 - **FAIL IF** the app accepts a non-canonical origin, a secret under 32 characters, or a success/error path off the application origin; inspect `authOptions` in `better-auth.ts`.
 
-Pinned by `integration/better-auth.test.ts`: `auth surface: explicit CSRF, exact origin, security headers and disabled unused endpoints`, `auth surface: an allowlisted write with a non-JSON body answers 415`, `auth options reject a non-canonical origin, a short secret and off-origin redirect paths`, `Better Auth email rejects expired codes and cross-origin sign-in`; `integration/better-auth-oauth.test.ts`: `Better Auth OAuth: Apple form_post relay, wrong browser, mismatched provider and expired state`, `Better Auth OAuth: callbacks refuse every method but GET and Apple's form-encoded POST`.
+Pinned by `integration/better-auth.test.ts`: `auth surface: explicit CSRF, exact origin, security headers and disabled unused endpoints`, `auth surface: an allowlisted write with a non-JSON body answers 415`, `auth options reject a non-canonical origin, a short secret and off-origin redirect paths`, `Better Auth email rejects expired codes and cross-origin sign-in`; `integration/better-auth-oauth.test.ts`: `Better Auth OAuth: Apple form_post relay, wrong browser, mismatched provider and expired state`, `Better Auth OAuth: callbacks refuse every method but GET and Apple's form-encoded POST`; `integration/better-auth-workers.test.ts`: `Workers auth setup failures return a safe 503 with security headers`.
 
 ## Email codes
 
diff --git a/packages/auth/src/better-auth-security.ts b/packages/auth/src/better-auth-security.ts
index e379502..a5939d7 100644
--- a/packages/auth/src/better-auth-security.ts
+++ b/packages/auth/src/better-auth-security.ts
@@ -1,6 +1,6 @@
 import { createHmac, timingSafeEqual } from 'node:crypto';
 import { sql } from 'kysely';
-import type { Hono } from 'hono';
+import type { Hono, MiddlewareHandler } from 'hono';
 import { isIdentityEmail } from './better-auth-email.ts';
 import { bodyLimit } from 'hono/body-limit';
 import type { connectDatabase } from 'pgstencil/postgres';
@@ -131,6 +131,20 @@ async function consume(
   return result.rows.length === 1;
 }
 
+/** Apply the same policy to auth responses and the Workers adapter's fallbacks. */
+export const authSecurityHeaders: MiddlewareHandler = async (c, next) => {
+  await next();
+  // Apply to the final response, including upstream immutable redirects.
+  c.header('Cache-Control', 'no-store');
+  c.header('Referrer-Policy', 'no-referrer');
+  c.header('X-Content-Type-Options', 'nosniff');
+  c.header('X-Frame-Options', 'DENY');
+  c.header(
+    'Content-Security-Policy',
+    "default-src 'none'; script-src 'self'; connect-src 'self'; form-action 'self'; base-uri 'none'; frame-ancestors 'none'",
+  );
+};
+
 export function protectAuth(
   app: Hono,
   options: {
@@ -170,18 +184,7 @@ export function protectAuth(
     c.req.raw = new Request(c.req.raw, { headers });
     await next();
   });
-  app.use('*', async (c, next) => {
-    await next();
-    // Apply to the final response, including upstream immutable redirects.
-    c.header('Cache-Control', 'no-store');
-    c.header('Referrer-Policy', 'no-referrer');
-    c.header('X-Content-Type-Options', 'nosniff');
-    c.header('X-Frame-Options', 'DENY');
-    c.header(
-      'Content-Security-Policy',
-      "default-src 'none'; script-src 'self'; connect-src 'self'; form-action 'self'; base-uri 'none'; frame-ancestors 'none'",
-    );
-  });
+  app.use('*', authSecurityHeaders);
   app.use('/api/auth/*', bodyLimit({ maxSize: 16 * 1024 }));
   app.get('/api/auth/csrf', (c) => {
     let value = cookies(c.req.raw).get(cookieName);
diff --git a/packages/auth/src/better-auth-workers.ts b/packages/auth/src/better-auth-workers.ts
index 9f73cc5..2a2fd38 100644
--- a/packages/auth/src/better-auth-workers.ts
+++ b/packages/auth/src/better-auth-workers.ts
@@ -6,6 +6,7 @@ import {
 import { Hono } from 'hono';
 import type { EmailSender } from 'pgstencil';
 import { createAuthApp, type AuthAppOptions } from './better-auth.ts';
+import { authSecurityHeaders } from './better-auth-security.ts';
 import {
   oauthFromEnvironment,
   providers,
@@ -41,6 +42,8 @@ export function createBetterAuthWorker<E extends BetterAuthWorkerBindings>(
   },
 ) {
   const app = new Hono<{ Bindings: E }>();
+  // Setup, teardown and diagnostics can return errors outside the inner app.
+  app.use('*', authSecurityHeaders);
   app.all('*', async (c) => {
     const handle = async () => {
       if (new URL(c.env.APP_ORIGIN).protocol !== 'https:')
diff --git a/tests/integration/better-auth-workers.test.ts b/tests/integration/better-auth-workers.test.ts
index 580fed3..5efc26b 100644
--- a/tests/integration/better-auth-workers.test.ts
+++ b/tests/integration/better-auth-workers.test.ts
@@ -180,6 +180,34 @@ async function login(f: Fixture, address = 'worker@example.test') {
   };
 }
 
+test('Workers auth setup failures return a safe 503 with security headers', async ({
+  onTestFinished,
+}) => {
+  const bundle = await bundles[0]!;
+  const worker = new Miniflare(
+    convertV4MiniflareOptions({
+      modules: true,
+      script: bundle.outputFiles[0]!.text,
+      compatibilityDate: '2026-09-08',
+      compatibilityFlags: ['nodejs_compat'],
+      bindings: { APP_ORIGIN: 'http://misconfigured.example.test' },
+    }),
+  );
+  onTestFinished(() => worker.dispose());
+  const response = await worker.dispatchFetch(origin + '/api/auth/get-session');
+  expect(response.status).toBe(503);
+  expect(response.headers.get('cache-control')).toBe('no-store');
+  expect(response.headers.get('referrer-policy')).toBe('no-referrer');
+  expect(response.headers.get('x-content-type-options')).toBe('nosniff');
+  expect(response.headers.get('x-frame-options')).toBe('DENY');
+  expect(response.headers.get('content-security-policy')).toBe(
+    "default-src 'none'; script-src 'self'; connect-src 'self'; form-action 'self'; base-uri 'none'; frame-ancestors 'none'",
+  );
+  expect(await response.json()).toEqual({
+    message: 'Sign-in is temporarily unavailable. Please try again.',
+  });
+});
+
 test('Better Auth in workerd: deterministic replay, separate clocks, shared database rate limits', async ({
   onTestFinished,
 }) => {
diff --git a/tests/unit/better-auth-workers.test.ts b/tests/unit/better-auth-workers.test.ts
new file mode 100644
index 0000000..8fbdc33
--- /dev/null
+++ b/tests/unit/better-auth-workers.test.ts
@@ -0,0 +1,51 @@
+import { test, expect } from 'vitest';
+import { createBetterAuthWorker } from '../../packages/auth/src/better-auth-workers.ts';
+import type { DiagnosticRecord } from '../../packages/pgstencil/src/diagnostics.ts';
+
+for (const diagnostics of [false, true])
+  for (const failure of ['insecure origin', 'email factory'])
+    test(`Workers auth errors keep security headers: ${failure}, diagnostics ${diagnostics}`, async () => {
+      const records: DiagnosticRecord[] = [];
+      const privateError = 'private-email@example.test secret-token';
+      const app = createBetterAuthWorker({
+        ...(diagnostics
+          ? {
+              diagnostics: {
+                sink: (record: DiagnosticRecord) => records.push(record),
+              },
+            }
+          : {}),
+        email: () => {
+          if (failure === 'email factory') throw new Error(privateError);
+          return { send: async () => {} };
+        },
+      });
+      const response = await app.fetch(
+        new Request('https://auth.example.test/api/auth/get-session'),
+        {
+          APP_ORIGIN: `${failure === 'insecure origin' ? 'http' : 'https'}://auth.example.test`,
+          AUTH_SECRET: 'worker-test-secret-at-least-32-characters',
+          HYPERDRIVE: { connectionString: 'postgres://unused' },
+        },
+      );
+      expect(response.status).toBe(503);
+      expect(response.headers.get('cache-control')).toBe('no-store');
+      expect(response.headers.get('referrer-policy')).toBe('no-referrer');
+      expect(response.headers.get('x-content-type-options')).toBe('nosniff');
+      expect(response.headers.get('x-frame-options')).toBe('DENY');
+      expect(response.headers.get('content-security-policy')).toBe(
+        "default-src 'none'; script-src 'self'; connect-src 'self'; form-action 'self'; base-uri 'none'; frame-ancestors 'none'",
+      );
+      expect(await response.json()).toEqual({
+        message: diagnostics
+          ? 'Temporarily unavailable. Please try again.'
+          : 'Sign-in is temporarily unavailable. Please try again.',
+      });
+      if (diagnostics) {
+        expect(response.headers.get('x-request-id')).toBeTruthy();
+        expect(
+          records.some((record) => record.event === 'request.failed'),
+        ).toBe(true);
+        expect(JSON.stringify(records)).not.toContain(privateError);
+      }
+    });