diff --git a/app/api/admin/__tests__/policy-if-match.test.ts b/app/api/admin/__tests__/policy-if-match.test.ts
index cc7bf3518..f98ce7b4f 100644
--- a/app/api/admin/__tests__/policy-if-match.test.ts
+++ b/app/api/admin/__tests__/policy-if-match.test.ts
@@ -101,4 +101,26 @@ describe('policy save with If-Match', () => {
     expect(res.status).toBe(200);
     expect((await stored()).features.calendarEnabled).toBe(false);
   });
+
+  it('answers 409 when the config manager was made by another bundle\'s copy of the module', async () => {
+    // In the server the instrumentation creates the config manager, so its
+    // errors are of the instrumentation's classes, not the route's.
+    const KEY = Symbol.for('bulwark.admin.configManager');
+    const g = globalThis as Record<symbol, unknown>;
+    const mine = g[KEY];
+    try {
+      delete g[KEY];
+      vi.resetModules();
+      await (await import('@/lib/admin/config-manager')).configManager.load();
+      vi.resetModules();
+      const route = await import('@/app/api/admin/policy/route');
+      const res = await route.GET(new NextRequest(URL));
+      const etag = res.headers.get('ETag')!;
+      await writeFile(path.join(dir, 'policy.json'), JSON.stringify({ features: { calendarEnabled: false } }));
+      const stale = await route.PUT(new NextRequest(URL, { method: 'PUT', headers: { 'if-match': etag }, body: JSON.stringify(await res.json()) }));
+      expect(stale.status).toBe(409);
+    } finally {
+      g[KEY] = mine;
+    }
+  });
 });
diff --git a/app/api/admin/policy/file/route.ts b/app/api/admin/policy/file/route.ts
index 62d7bee0c..d4dca9ef1 100644
--- a/app/api/admin/policy/file/route.ts
+++ b/app/api/admin/policy/file/route.ts
@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
-import { completePolicy, configManager, PolicyConflictError } from '@/lib/admin/config-manager';
+import { completePolicy, configManager, isPolicyConflict } from '@/lib/admin/config-manager';
 import { requireAdminAuth, getClientIP } from '@/lib/admin/session';
 import { auditLog } from '@/lib/admin/audit';
 import { logger } from '@/lib/logger';
@@ -71,7 +71,7 @@ export async function POST(request: NextRequest) {
         await configManager.setPolicy(next, { ifVersion: version });
         break;
       } catch (error) {
-        if (!(error instanceof PolicyConflictError)) throw error;
+        if (!isPolicyConflict(error)) throw error;
         if (attempt >= 3) return NextResponse.json({ error: error.message }, { status: 409 });
       }
     }
diff --git a/app/api/admin/policy/route.ts b/app/api/admin/policy/route.ts
index 512307784..a799231df 100644
--- a/app/api/admin/policy/route.ts
+++ b/app/api/admin/policy/route.ts
@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
-import { configManager, PolicyConflictError } from '@/lib/admin/config-manager';
+import { configManager, isPolicyConflict } from '@/lib/admin/config-manager';
 import { requireAdminAuth, getClientIP } from '@/lib/admin/session';
 import { auditLog } from '@/lib/admin/audit';
 import { logger } from '@/lib/logger';
@@ -135,7 +135,7 @@ export async function PUT(request: NextRequest) {
     try {
       version = await configManager.setPolicy(policy, { ifVersion: ifMatchVersion(request) });
     } catch (error) {
-      if (error instanceof PolicyConflictError) {
+      if (isPolicyConflict(error)) {
         return NextResponse.json({ error: error.message }, { status: 409 });
       }
       throw error;
diff --git a/lib/admin/config-manager.ts b/lib/admin/config-manager.ts
index a540c7f11..5ffe686eb 100644
--- a/lib/admin/config-manager.ts
+++ b/lib/admin/config-manager.ts
@@ -59,6 +59,15 @@ export class PolicyConflictError extends Error {
   }
 }
 
+/**
+ * Whether `error` is a PolicyConflictError. By name, not instanceof: the
+ * config manager on globalThis may come from another bundle's copy of this
+ * module (the instrumentation creates it), whose class is a different object.
+ */
+export function isPolicyConflict(error: unknown): error is PolicyConflictError {
+  return error instanceof Error && error.name === 'PolicyConflictError';
+}
+
 /** Policy writes in this process, one after another, so a version check and its write can't interleave. */
 const POLICY_WRITE_QUEUE = 'admin-config\0policy.json';