diff --git a/server/package.json b/server/package.json
index 1792323..6415318 100644
--- a/server/package.json
+++ b/server/package.json
@@ -11,7 +11,8 @@
     "dev": "node --watch src/index.js",
     "start": "node src/index.js",
     "test": "vitest run",
-    "prisma:generate": "prisma generate"
+    "prisma:generate": "prisma generate",
+    "fix:demo-role": "node prisma/downgradeDemoAdmin.js"
   },
   "dependencies": {
     "@prisma/client": "^5.22.0",
diff --git a/server/prisma/downgradeDemoAdmin.js b/server/prisma/downgradeDemoAdmin.js
new file mode 100644
index 0000000..ad6a400
--- /dev/null
+++ b/server/prisma/downgradeDemoAdmin.js
@@ -0,0 +1,41 @@
+// Targeted, idempotent remediation script for the demo account privilege
+// exposure (issue #55): downgrades demo@lexforge.app to role 'user' if it
+// currently has an elevated role, without touching any other data. Safe to
+// run repeatedly against prod. Import-safe: only executes when run directly
+// (`node prisma/downgradeDemoAdmin.js`), never as a side effect of importing
+// this module.
+
+import { pathToFileURL } from 'node:url';
+import { PrismaClient } from '@prisma/client';
+import { DEMO_USER_EMAIL } from './seed.js';
+
+export async function downgradeDemoAdmin(prisma) {
+  const existing = await prisma.user.findUnique({ where: { email: DEMO_USER_EMAIL } });
+  if (!existing) {
+    console.log(`No user found for ${DEMO_USER_EMAIL}; nothing to downgrade.`);
+    return null;
+  }
+
+  const user = await prisma.user.update({
+    where: { email: DEMO_USER_EMAIL },
+    data: { role: 'user' },
+  });
+
+  return user.role;
+}
+
+// Only run when executed directly (`node prisma/downgradeDemoAdmin.js`),
+// never as a side effect of importing this module.
+if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
+  const prisma = new PrismaClient();
+  downgradeDemoAdmin(prisma)
+    .then((role) => {
+      console.log(`Demo user role is now: ${role}`);
+    })
+    .then(() => prisma.$disconnect())
+    .catch(async (error) => {
+      console.error(error);
+      await prisma.$disconnect();
+      process.exit(1);
+    });
+}
diff --git a/server/prisma/downgradeDemoAdmin.test.js b/server/prisma/downgradeDemoAdmin.test.js
new file mode 100644
index 0000000..6d27483
--- /dev/null
+++ b/server/prisma/downgradeDemoAdmin.test.js
@@ -0,0 +1,52 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { createFakePrismaClient } from '../test-utils/fakePrismaClient.js';
+import { downgradeDemoAdmin } from './downgradeDemoAdmin.js';
+import { DEMO_USER_EMAIL } from './seed.js';
+
+describe('downgradeDemoAdmin', () => {
+  let prisma;
+
+  beforeEach(() => {
+    prisma = createFakePrismaClient();
+  });
+
+  it('downgrades an existing demo admin user to role "user"', async () => {
+    await prisma.user.create({
+      data: {
+        email: DEMO_USER_EMAIL,
+        passwordHash: 'irrelevant-hash',
+        name: 'Demo User',
+        role: 'admin',
+      },
+    });
+
+    const role = await downgradeDemoAdmin(prisma);
+
+    expect(role).toBe('user');
+
+    const user = await prisma.user.findUnique({ where: { email: DEMO_USER_EMAIL } });
+    expect(user.role).toBe('user');
+  });
+
+  it('is idempotent when run a second time', async () => {
+    await prisma.user.create({
+      data: {
+        email: DEMO_USER_EMAIL,
+        passwordHash: 'irrelevant-hash',
+        name: 'Demo User',
+        role: 'admin',
+      },
+    });
+
+    await downgradeDemoAdmin(prisma);
+    const role = await downgradeDemoAdmin(prisma);
+
+    expect(role).toBe('user');
+  });
+
+  it('does not throw when the demo user does not exist', async () => {
+    const role = await downgradeDemoAdmin(prisma);
+
+    expect(role).toBeNull();
+  });
+});
diff --git a/server/prisma/seed.js b/server/prisma/seed.js
index a019edb..ca7eba0 100644
--- a/server/prisma/seed.js
+++ b/server/prisma/seed.js
@@ -352,7 +352,7 @@ export async function seed(prisma) {
 
   const user = await prisma.user.upsert({
     where: { email: DEMO_USER_EMAIL },
-    update: {},
+    update: { role: 'user' },
     create: {
       email: DEMO_USER_EMAIL,
       passwordHash,
@@ -411,3 +411,5 @@ if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href)
       process.exit(1);
     });
 }
+
+export { DEMO_USER_EMAIL };
diff --git a/server/prisma/seed.test.js b/server/prisma/seed.test.js
index c7fbb5c..3c91c1f 100644
--- a/server/prisma/seed.test.js
+++ b/server/prisma/seed.test.js
@@ -57,4 +57,19 @@ describe('seed function', () => {
     expect(user.email).toBe('demo@lexforge.app');
     expect(user.role).toBe('user');
   });
+
+  it('should downgrade an existing demo admin user to role "user" when re-run', async () => {
+    await prisma.user.create({
+      data: {
+        email: 'demo@lexforge.app',
+        passwordHash: 'irrelevant-hash',
+        name: 'Demo User',
+        role: 'admin',
+      },
+    });
+
+    const { user } = await seed(prisma);
+
+    expect(user.role).toBe('user');
+  });
 });
diff --git a/server/test-utils/fakePrismaClient.js b/server/test-utils/fakePrismaClient.js
index 18de772..7f13737 100644
--- a/server/test-utils/fakePrismaClient.js
+++ b/server/test-utils/fakePrismaClient.js
@@ -91,7 +91,9 @@ function createFakeModel({ uniqueFields = [] } = {}) {
     },
 
     async update({ where, data }) {
-      const existing = where.id !== undefined ? rows.get(where.id) : undefined;
+      const existing = where.id !== undefined
+        ? rows.get(where.id)
+        : [...rows.values()].find((r) => matchesWhere(r, where));
       if (!existing) {
         throw new Error(`Record not found for update: ${JSON.stringify(where)}`);
       }