diff --git a/src/main-node.ts b/src/main-node.ts
index 9aa9493077..67b99b5691 100644
--- a/src/main-node.ts
+++ b/src/main-node.ts
@@ -10,7 +10,7 @@ export const requestHandlers = {
       process.platform === 'win32'
         ? decodeURI(fileURL.pathname).substring(1)
         : decodeURI(fileURL.pathname)
-    const f = await fs.open(filePath, 'rb')
+    const f = await fs.open(filePath, 'r')
     let contents: Buffer, ok: boolean
     if (typeof o.length !== 'undefined' && typeof o.offset !== 'undefined') {
       contents = Buffer.alloc(o.length)
diff --git a/test/main/filesystem-api.test.ts b/test/main/filesystem-api.test.ts
new file mode 100644
index 0000000000..b7474fdc72
--- /dev/null
+++ b/test/main/filesystem-api.test.ts
@@ -0,0 +1,57 @@
+import { describe, test, before, after } from 'node:test'
+import path from 'node:path'
+import os from 'node:os'
+import fs from 'node:fs'
+import assert from 'node:assert'
+import { pipeline } from 'node:stream/promises'
+import { fetch } from 'undici'
+import { normalize, config } from '../../src/main-node'
+import { assertMatchCloseTo } from '../helpers'
+
+async function downloadFile(file: string, destDir: string) {
+  const resp = await fetch(`https://japanese-addresses-v2.geoloniamaps.com/api/${file}`)
+  const outputFile = path.join(destDir, file)
+  await fs.promises.mkdir(path.dirname(outputFile), { recursive: true })
+  const writer = fs.createWriteStream(outputFile)
+  if (!resp.body) { throw new Error('No body') }
+  await pipeline(resp.body, writer)
+}
+
+describe(`API stored in filesystem`, () => {
+  let tmpdir: string
+  before(async () => {
+    tmpdir = await fs.promises.mkdtemp(path.join(os.tmpdir(), 'qtile-update-csv-'))
+    const files = [
+      'ja.json',
+      'ja/東京都/渋谷区.json',
+      'ja/東京都/渋谷区-住居表示.txt',
+    ]
+    for (const file of files) {
+      await downloadFile(file, tmpdir)
+    }
+
+    config.japaneseAddressesApi = `file://${tmpdir}/ja`
+  })
+
+  after(async () => {
+    await fs.promises.rm(tmpdir, { recursive: true, force: true })
+  })
+
+  test(`基本的に動く`, async () => {
+    const res = await normalize('渋谷区道玄坂1-10-8')
+    assertMatchCloseTo(res, {
+      pref: '東京都',
+      city: '渋谷区',
+      town: '道玄坂一丁目',
+      level: 8,
+    })
+  })
+
+  test(`用意されていないエリアはエラーになる`, async () => {
+    try {
+      await normalize('東京都千代田区')
+    } catch (e) {
+      assert.strictEqual(e.code, 'ENOENT')
+    }
+  })
+})