diff --git a/src/adapters/normalized-adapter.test.ts b/src/adapters/normalized-adapter.test.ts
index 67f85a3ec..18fe363a6 100644
--- a/src/adapters/normalized-adapter.test.ts
+++ b/src/adapters/normalized-adapter.test.ts
@@ -51,6 +51,16 @@ await test('read removes $schema and normalizes ids', async () => {
   assert.notEqual(posts[1]?.['id'], '')
 })
 
+await test('read preserves primitive array items', async () => {
+  const adapter = new StubAdapter({
+    roles: ['admin', 'user'],
+  })
+
+  const normalized = await new NormalizedAdapter(adapter).read()
+
+  assert.deepEqual(normalized?.['roles'], ['admin', 'user'])
+})
+
 await test('write always overwrites $schema', async () => {
   const adapter = new StubAdapter(null)
   const normalizedAdapter = new NormalizedAdapter(adapter)
diff --git a/src/adapters/normalized-adapter.ts b/src/adapters/normalized-adapter.ts
index e2d9e7284..ba01a1a67 100644
--- a/src/adapters/normalized-adapter.ts
+++ b/src/adapters/normalized-adapter.ts
@@ -1,10 +1,10 @@
 import type { Adapter } from 'lowdb'
 
 import { randomId } from '../random-id.ts'
-import type { Data, Item } from '../service.ts'
+import { isItem, type Data, type Item } from '../service.ts'
 
 export const DEFAULT_SCHEMA_PATH = './node_modules/json-server/schema.json'
-export type RawData = Record<string, Item[] | Item | string | undefined> & {
+export type RawData = Record<string, Item[] | Item | string | unknown[] | undefined> & {
   $schema?: string
 }
 
@@ -27,6 +27,10 @@ export class NormalizedAdapter implements Adapter<Data> {
     for (const value of Object.values(data)) {
       if (Array.isArray(value)) {
         for (const item of value) {
+          if (!isItem(item)) {
+            continue
+          }
+
           if (typeof item['id'] === 'number') {
             item['id'] = item['id'].toString()
           }
diff --git a/src/bin.ts b/src/bin.ts
index 3cc39d83b..7a10c68f4 100644
--- a/src/bin.ts
+++ b/src/bin.ts
@@ -16,6 +16,7 @@ import { NormalizedAdapter } from "./adapters/normalized-adapter.ts";
 import type { RawData } from "./adapters/normalized-adapter.ts";
 import { Observer } from "./adapters/observer.ts";
 import { createApp } from "./app.ts";
+import { formatPrimitiveArrayWarning, primitiveArrayResourceNames } from "./primitive-array-warning.ts";
 import type { Data } from "./service.ts";
 
 function help() {
@@ -139,6 +140,10 @@ const observer = new Observer(new NormalizedAdapter(adapter));
 const db = new Low<Data>(observer, {});
 await db.read();
 
+for (const name of primitiveArrayResourceNames(db.data)) {
+  console.log(chalk.yellow(formatPrimitiveArrayWarning(name)));
+}
+
 // Create app
 const app = createApp(db, { logger: false, static: staticArr });
 
diff --git a/src/primitive-array-warning.test.ts b/src/primitive-array-warning.test.ts
new file mode 100644
index 000000000..c2fee7857
--- /dev/null
+++ b/src/primitive-array-warning.test.ts
@@ -0,0 +1,26 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+
+import type { Data } from './service.ts'
+import {
+  formatPrimitiveArrayWarning,
+  primitiveArrayResourceNames,
+} from './primitive-array-warning.ts'
+
+await test('primitiveArrayResourceNames returns resources with primitive array items', () => {
+  const data = {
+    roles: ['admin', 'user'],
+    posts: [{ id: '1', title: 'post' }],
+    mixed: [{ id: '1' }, null],
+    profile: { name: 'Ada' },
+  } as unknown as Data
+
+  assert.deepEqual(primitiveArrayResourceNames(data), ['roles', 'mixed'])
+})
+
+await test('formatPrimitiveArrayWarning describes the resource problem', () => {
+  assert.equal(
+    formatPrimitiveArrayWarning('roles'),
+    'Warning: "roles" contains primitive values. Resources should usually be arrays of objects with id fields.',
+  )
+})
diff --git a/src/primitive-array-warning.ts b/src/primitive-array-warning.ts
new file mode 100644
index 000000000..d518c38b3
--- /dev/null
+++ b/src/primitive-array-warning.ts
@@ -0,0 +1,15 @@
+import { isItem, type Data } from './service.ts'
+
+export function primitiveArrayResourceNames(data: Data): string[] {
+  return Object.entries(data).flatMap(([name, value]) => {
+    if (Array.isArray(value) && value.some((item: unknown) => !isItem(item))) {
+      return [name]
+    }
+
+    return []
+  })
+}
+
+export function formatPrimitiveArrayWarning(name: string): string {
+  return `Warning: "${name}" contains primitive values. Resources should usually be arrays of objects with id fields.`
+}