diff --git a/src/lib/badge-editor-upload.ts b/src/lib/badge-editor-upload.ts
index 929715c..e8d5510 100644
--- a/src/lib/badge-editor-upload.ts
+++ b/src/lib/badge-editor-upload.ts
@@ -13,6 +13,17 @@ export type DiskDirectory = {
   removeEntry: (name: string, options?: { recursive?: boolean }) => Promise<void>
 }
 
+export async function validateBadgeRoot(root: DiskDirectory) {
+  try {
+    await root.getDirectoryHandle('apps')
+  } catch (error) {
+    if (error instanceof DOMException && (error.name === 'NotFoundError' || error.name === 'TypeMismatchError')) {
+      throw new Error('Select the BADGER USB volume itself, rather than an app folder. The selected folder must contain the apps directory.')
+    }
+    throw error
+  }
+}
+
 export class ExistingAppError extends Error {
   constructor() {
     super('This app already exists. Open it from the badge to edit, or allow updating this app and click Upload again.')
diff --git a/src/lib/badge-editor.ts b/src/lib/badge-editor.ts
index 11550b7..a094423 100644
--- a/src/lib/badge-editor.ts
+++ b/src/lib/badge-editor.ts
@@ -1,4 +1,4 @@
-import { ExistingAppError, uploadEditorProject, validateAppName, type DiskDirectory } from './badge-editor-upload'
+import { ExistingAppError, uploadEditorProject, validateAppName, validateBadgeRoot, type DiskDirectory } from './badge-editor-upload'
 import { initEditorSplit } from './badge-editor-split'
 import { initProjectPicker } from './badge-editor-picker'
 import { initEditorFullscreen } from './badge-editor-fullscreen'
@@ -494,8 +494,7 @@ export async function initBadgeEditor() {
     setBusy(true)
     try {
       const root = await picker.call(window, { mode: 'readwrite' })
-      if (root.name.toUpperCase() !== 'BADGER') throw new Error('Select the BADGER USB volume itself, rather than an app folder.')
-      await root.getDirectoryHandle('apps')
+      await validateBadgeRoot(root)
       const oldDisk = disk
       disk = root
       try { await refreshDeviceApps() } catch (error) { disk = oldDisk; throw error }
diff --git a/tests/badge-editor-upload.test.mjs b/tests/badge-editor-upload.test.mjs
index 6dd4673..0f551cc 100644
--- a/tests/badge-editor-upload.test.mjs
+++ b/tests/badge-editor-upload.test.mjs
@@ -5,7 +5,43 @@ import { build } from 'esbuild'
 
 const compiled = await build({ entryPoints: [fileURLToPath(new URL('../src/lib/badge-editor-upload.ts', import.meta.url))], bundle: true, format: 'esm', platform: 'node', write: false })
 const moduleUrl = `data:text/javascript;base64,${Buffer.from(compiled.outputFiles[0].text).toString('base64')}`
-const { uploadEditorApp, uploadEditorProject, ExistingAppError } = await import(moduleUrl)
+const { uploadEditorApp, uploadEditorProject, validateBadgeRoot, ExistingAppError } = await import(moduleUrl)
+
+test('badge root validation accepts Windows drive names and renamed volumes without writing', async () => {
+  for (const name of ['BADGER', 'E:', 'E:\\', 'BADGER (E:)', 'MY-BADGE']) {
+    const checked = []
+    await validateBadgeRoot({
+      name,
+      async getDirectoryHandle(path, options) {
+        checked.push(path)
+        assert.equal(options, undefined)
+        return {}
+      },
+    })
+    assert.deepEqual(checked, ['apps'])
+  }
+})
+
+test('badge root validation rejects app folders and volumes without an apps directory', async () => {
+  for (const name of ['my-app', 'apps', 'BADGER', 'RP2350', 'E:']) {
+    for (const errorName of ['NotFoundError', 'TypeMismatchError']) {
+      await assert.rejects(validateBadgeRoot({
+        name,
+        async getDirectoryHandle() { throw new DOMException('Invalid apps directory', errorName) },
+      }), /Select the BADGER USB volume itself/)
+    }
+  }
+})
+
+test('badge root validation preserves permission and device errors', async () => {
+  for (const errorName of ['NotAllowedError', 'NotReadableError']) {
+    const error = new DOMException('Cannot read device', errorName)
+    await assert.rejects(validateBadgeRoot({
+      name: 'E:',
+      async getDirectoryHandle() { throw error },
+    }), thrown => thrown === error)
+  }
+})
 
 function filesystem(existing = false, failure = '') {
   const files = new Map(existing ? [['__init__.py', 'original'], ['icon.png', 'icon']] : [])