diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index c85a7c84f..ad5592ec4 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -67,3 +67,26 @@ jobs:
 
       - name: Lint
         run: npm run lint
+
+  # The build the release tarball and a manual install use, with its guard at
+  # the end. Docker and the Lite images build another way (webpack, export), so
+  # nothing else would notice this one breaking before a release does.
+  standalone-build:
+    name: Standalone build and guard
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+
+      - name: Set up Node
+        uses: actions/setup-node@v7
+        with:
+          node-version: 22
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run build
diff --git a/lib/desktop/__tests__/trust-flag.test.ts b/lib/desktop/__tests__/trust-flag.test.ts
index c40bd5846..0edd41532 100644
--- a/lib/desktop/__tests__/trust-flag.test.ts
+++ b/lib/desktop/__tests__/trust-flag.test.ts
@@ -3,7 +3,7 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { readFileSync } from 'node:fs';
 import path from 'node:path';
 import { build } from 'esbuild';
-import { desktopBuildFlag } from '../../../scripts/desktop-build-flag.mjs';
+import { DESKTOP_TRUST_MARKER, desktopBuildFlag } from '../../../scripts/desktop-build-flag.mjs';
 
 const ROOT = path.resolve(__dirname, '../../..');
 const TRUST_KEY = Symbol.for('bulwark.desktop.trustedJmapOrigins');
@@ -112,6 +112,28 @@ describe('the flag is fixed at build time', () => {
     }
   });
 
+  /** Compiles the trust check alone, kept as an export the way Turbopack keeps it. */
+  async function trustCheckOfBuild(flag: string): Promise<string> {
+    const result = await build({
+      entryPoints: [path.join(ROOT, 'lib/desktop/trusted-servers.ts')],
+      bundle: true,
+      write: false,
+      minify: true,
+      format: 'esm',
+      platform: 'node',
+      define: { 'process.env.NEXT_PUBLIC_BULWARK_DESKTOP': JSON.stringify(flag) },
+    });
+    return result.outputFiles[0].text;
+  }
+
+  it('a server build holds no trust path, even when a bundler keeps the unused export', async () => {
+    expect(await trustCheckOfBuild('')).not.toContain(DESKTOP_TRUST_MARKER);
+  });
+
+  it('a desktop build still holds it', async () => {
+    expect(await trustCheckOfBuild('1')).toContain(DESKTOP_TRUST_MARKER);
+  });
+
   it('no image build sets it', () => {
     for (const file of ['Dockerfile', 'Dockerfile.lite']) {
       expect(readFileSync(path.join(ROOT, file), 'utf8')).not.toContain('NEXT_PUBLIC_BULWARK_DESKTOP');
diff --git a/lib/desktop/trusted-servers.ts b/lib/desktop/trusted-servers.ts
index e2cf034b5..8fa60c651 100644
--- a/lib/desktop/trusted-servers.ts
+++ b/lib/desktop/trusted-servers.ts
@@ -7,8 +7,9 @@
  * or the environment can write it, so script in a page can't aim the login
  * routes at the LAN.
  *
- * Callers guard this with IS_DESKTOP_BUILD, so a server build compiles the
- * whole thing away. scripts/standalone-guard.mjs checks that it did.
+ * Callers check the flag too, but Turbopack keeps an imported export after the
+ * call is gone. So the check also starts here, spelled out: every bundler then
+ * drops the body from a server build. scripts/standalone-guard.mjs checks it did.
  */
 
 type TrustedOrigins = ReadonlySet<string>;
@@ -25,6 +26,7 @@ function originOf(url: string): string | null {
 }
 
 export function isDesktopTrustedServer(url: string | null | undefined): boolean {
+  if (process.env.NEXT_PUBLIC_BULWARK_DESKTOP !== '1') return false;
   if (!url) return false;
   const origin = originOf(url);
   if (!origin) return false;