diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 99039d9..0e0f922 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -15,7 +15,7 @@ import { msToTime } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
 import { useUITranslation } from '@/lib/useUITranslation'
 
-import type { FC, FormEvent } from 'react'
+import type { FC, FormEvent, ReactNode } from 'react'
 
 import type { Post, TagWithSections } from '@/types'
 
@@ -23,6 +23,8 @@ type PostFormField =
     'parentPostIds' | 'tags' | 'videoMs'
     | 'originalCreatedAt' | 'originalCreatedFrom' | 'originalCreatedBefore'
 
+type PostEditData = Omit<Parameters<typeof updatePost>[0], 'id'>
+
 const groupedMessages = (...values: (string[] | undefined)[]): string[] =>
     [...new Set (values.flatMap (value => value ?? []))]
 
@@ -150,12 +152,63 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
   const handleSubmit = async (e: FormEvent) => {
     e.preventDefault ()
 
+    if (disabled) return
+
     setDisabled (true)
     try
     {
-      await update ({ id: post.id, title, tags, parentPostIds,
-		      duration: videoFlg ? duration : null,
-		      originalCreatedFrom, originalCreatedBefore },
+      const current: PostEditData = {
+	  title, tags, parentPostIds,
+	  duration: videoFlg ? duration : null,
+	  originalCreatedFrom, originalCreatedBefore }
+      const fields: {
+	  [Key in keyof PostEditData]-?: {
+	      name: ReactNode
+	      prev: PostEditData[Key] } } = {
+	  title: { name: label ('shared:labels.title'), prev: post.title },
+	  parentPostIds: {
+	      name: label ('shared:labels.parentPosts'),
+	      prev: (post.parentPosts ?? []).map (parent => parent.id).join (' ') },
+	  tags: { name: label ('tags:title'), prev: tagsToStr (post.tags) },
+	  duration: {
+	      name: label ('shared:labels.duration'),
+	      prev: videoMsToDurationValue (post.videoMs) },
+	  originalCreatedFrom: {
+	      name: <>{label ('shared:labels.originalCreatedAt')}{' '}
+			{label ('shared:labels.since')}</>,
+	      prev: post.originalCreatedFrom },
+	  originalCreatedBefore: {
+	      name: <>{label ('shared:labels.originalCreatedAt')}{' '}
+			{label ('shared:labels.before')}</>,
+	      prev: post.originalCreatedBefore } }
+      const differences = (Object.keys (fields) as (keyof PostEditData)[])
+	  .map (key => ({ key, name: fields[key].name,
+	      prev: fields[key].prev ?? '', current: current[key] ?? '' }))
+	  .filter (row => row.prev !== row.current)
+
+      if (!(await dialogue.confirm ({
+	  title: label ('shared:actions.diff'),
+	  confirmText: label ('shared:actions.update'),
+	  description: (
+	      <dl className="max-h-[60dvh] overflow-y-auto space-y-3 text-left">
+		{differences.map (row => (
+		    <div key={row.key}>
+		      <dt className="font-semibold">{row.name}</dt>
+		      <dd className="whitespace-pre-wrap break-words">
+			{row.prev && (
+			    <del className="block text-red-600 dark:text-red-400">
+			      {row.prev}
+			    </del>)}
+			{row.current && (
+			    <ins className="block text-green-700 dark:text-green-400">
+			      {row.current}
+			    </ins>)}
+		      </dd>
+		    </div>))}
+	      </dl>) })))
+	return
+
+      await update ({ id: post.id, ...current },
 		    { baseVersionNo: post.versionNo })
     }
     finally