diff --git a/frontend/src/components/PostEditForm.test.tsx b/frontend/src/components/PostEditForm.test.tsx
index 60c4170..395c789 100644
--- a/frontend/src/components/PostEditForm.test.tsx
+++ b/frontend/src/components/PostEditForm.test.tsx
@@ -1,11 +1,13 @@
-import { fireEvent, screen, waitFor } from '@testing-library/react'
-import { describe, expect, it, vi } from 'vitest'
+import { act, fireEvent, screen, waitFor } from '@testing-library/react'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { textContentOf } from '@/test/text'
 import PostEditForm from '@/components/PostEditForm'
 import { buildPost, buildTag } from '@/test/factories'
 import { renderWithProviders as render } from '@/test/render'
 
+import type { DialogueAPI } from '@/lib/dialogues/useDialogue'
+
 const postsApi = vi.hoisted (() => ({
   updatePost: vi.fn (),
 }))
@@ -18,18 +20,27 @@ const toastApi = vi.hoisted (() => ({
   toast: vi.fn (),
 }))
 
+const dialogue = vi.hoisted (() => ({
+    confirm: vi.fn<DialogueAPI['confirm']> (),
+    choice: vi.fn () }))
+
 vi.mock ('@/lib/posts', () => postsApi)
 vi.mock ('@/lib/api', () => api)
 vi.mock ('@/components/ui/use-toast', () => toastApi)
 vi.mock ('@/lib/dialogues/useDialogue', async importOriginal => ({
-  ...await importOriginal<typeof import ('@/lib/dialogues/useDialogue')> (),
-  default: () => ({
-    choice: vi.fn (),
-  }),
-}))
+    ...await importOriginal<typeof import ('@/lib/dialogues/useDialogue')> (),
+    default: () => dialogue }))
 
 describe ('PostEditForm', () => {
+  beforeEach (() => {
+    vi.resetAllMocks ()
+  })
+
   it ('submits edited post fields with the current base version', async () => {
+    const confirm = vi.fn<(value: boolean) => void> ()
+    dialogue.confirm.mockReturnValueOnce (new Promise<boolean> (resolve => {
+      confirm.mockImplementation (resolve)
+    }))
     const onSave = vi.fn ()
     const post = buildPost ({
       id:        8,
@@ -55,6 +66,16 @@ describe ('PostEditForm', () => {
     fireEvent.change (parentIds, { target: { value: '3 4' } })
     fireEvent.submit (screen.getByRole ('button', { name: '更新' }).closest ('form')!)
 
+    expect (postsApi.updatePost).not.toHaveBeenCalled ()
+    expect (dialogue.confirm).toHaveBeenCalledTimes (1)
+    const difference = textContentOf (
+	dialogue.confirm.mock.calls[0][0].description)
+    expect (difference).toContain ('oldnew')
+    expect (difference).toContain ('23 4')
+    expect (difference).not.toContain ('general-tag')
+
+    await act (async () => { confirm (true) })
+
     await waitFor (() => {
       expect (postsApi.updatePost).toHaveBeenCalledWith (
           expect.objectContaining ({
@@ -71,6 +92,28 @@ describe ('PostEditForm', () => {
     expect (textContentOf (toastApi.toast.mock.calls[0][0].description)).toBe ('更新しました．')
   })
 
+  it ('keeps edited fields without submitting when confirmation is cancelled', async () => {
+    const onSave = vi.fn ()
+    dialogue.confirm.mockResolvedValueOnce (false)
+    render (<PostEditForm post={buildPost ()} onSave={onSave}/>)
+
+    const [title, parentIds] = screen.getAllByRole ('textbox')
+    fireEvent.change (title, { target: { value: 'new' } })
+    fireEvent.change (parentIds, { target: { value: '3 4' } })
+    const button = screen.getByRole ('button', { name: '更新' })
+    fireEvent.submit (button.closest ('form')!)
+
+    await waitFor (() => {
+      expect (button).toBeEnabled ()
+    })
+    expect (dialogue.confirm).toHaveBeenCalledTimes (1)
+    expect (postsApi.updatePost).not.toHaveBeenCalled ()
+    expect (onSave).not.toHaveBeenCalled ()
+    expect (toastApi.toast).not.toHaveBeenCalled ()
+    expect (title).toHaveValue ('new')
+    expect (parentIds).toHaveValue ('3 4')
+  })
+
   it ('preserves duration while the video tag is temporarily removed', () => {
     const post = buildPost ({
       videoMs: 180_500,
@@ -100,6 +143,7 @@ describe ('PostEditForm', () => {
       'shows deduplicated original-created endpoint errors on the shared datetime field',
       async () => {
     const post = buildPost ()
+    dialogue.confirm.mockResolvedValueOnce (true)
     api.isApiError.mockReturnValue (true)
     postsApi.updatePost.mockRejectedValueOnce ({
       response: {