diff --git a/frontend/src/components/posts/PostThumbnailPreview.test.tsx b/frontend/src/components/posts/PostThumbnailPreview.test.tsx
index 0ff9070..bb9a17e 100644
--- a/frontend/src/components/posts/PostThumbnailPreview.test.tsx
+++ b/frontend/src/components/posts/PostThumbnailPreview.test.tsx
@@ -1,4 +1,4 @@
-import { render, screen } from '@testing-library/react'
+import { fireEvent, render, screen } from '@testing-library/react'
 import { describe, expect, it } from 'vitest'
 
 import PostThumbnailPreview from '@/components/posts/PostThumbnailPreview'
@@ -9,4 +9,28 @@ describe ('PostThumbnailPreview', () => {
 
     expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:preview')
   })
+
+  it ('renders an empty thumbnail frame without text when the URL is empty', () => {
+    const { container } = render (
+        <PostThumbnailPreview url="" className="h-10 w-10"/>)
+
+    expect (screen.queryByRole ('img')).toBeNull ()
+    expect (screen.queryByText ('サムネールを表示できません')).toBeNull ()
+    expect (screen.queryByText ('なし')).toBeNull ()
+    expect (container.querySelector ('div.rounded.border.bg-muted')).not.toBeNull ()
+    expect (container.textContent).toBe ('')
+  })
+
+  it ('renders an empty thumbnail frame without text when image loading fails', () => {
+    const { container } = render (
+        <PostThumbnailPreview url="blob:preview" className="h-10 w-10"/>)
+
+    fireEvent.error (screen.getByRole ('img'))
+
+    expect (screen.queryByRole ('img')).toBeNull ()
+    expect (screen.queryByText ('サムネールを表示できません')).toBeNull ()
+    expect (screen.queryByText ('なし')).toBeNull ()
+    expect (container.querySelector ('div.rounded.border.bg-muted')).not.toBeNull ()
+    expect (container.textContent).toBe ('')
+  })
 })
diff --git a/frontend/src/components/posts/PostThumbnailPreview.tsx b/frontend/src/components/posts/PostThumbnailPreview.tsx
index 099ef2c..6b2a990 100644
--- a/frontend/src/components/posts/PostThumbnailPreview.tsx
+++ b/frontend/src/components/posts/PostThumbnailPreview.tsx
@@ -19,30 +19,13 @@ const PostThumbnailPreview: FC<Props> = (
     setFailed (false)
   }, [url])
 
-  if (!(url))
+  if (!(url) || failed)
     {
       return (
           <div
               className={cn (
                   className,
-                  'flex items-center justify-center rounded border',
-                  'border-border bg-muted text-xs text-muted-foreground')}>
-            なし
-          </div>)
-    }
-
-  if (failed)
-    {
-      return (
-          <div
-              className={cn (
-                  className,
-                  'flex items-center justify-center rounded border',
-                  'border-amber-300 bg-amber-50 p-2 text-center text-xs',
-                  'text-amber-700 dark:border-amber-900 dark:bg-amber-950',
-                  'dark:text-amber-200')}>
-            サムネールを表示できません
-          </div>)
+                  'rounded border border-border bg-muted')}/>)
     }
 
   return (
diff --git a/frontend/src/components/posts/import/PostImportThumbnailPreview.test.tsx b/frontend/src/components/posts/import/PostImportThumbnailPreview.test.tsx
index 21cdd0c..16a3ed4 100644
--- a/frontend/src/components/posts/import/PostImportThumbnailPreview.test.tsx
+++ b/frontend/src/components/posts/import/PostImportThumbnailPreview.test.tsx
@@ -38,12 +38,18 @@ describe ('PostImportThumbnailPreview', () => {
   it ('does not render the unsafe URL directly when preview fetching fails', async () => {
     api.apiGet.mockRejectedValueOnce (new Error ('unsafe'))
 
-    render (
+    const { container } = render (
         <PostImportThumbnailPreview
             url="http://127.0.0.1/private.png"
             className="h-10 w-10"/>)
 
-    expect (await screen.findByText ('サムネールを表示できません')).toBeInTheDocument ()
+    await waitFor (() => {
+      expect (screen.queryByRole ('img')).toBeNull ()
+    })
+    expect (screen.queryByText ('サムネールを表示できません')).toBeNull ()
+    expect (screen.queryByText ('なし')).toBeNull ()
+    expect (container.querySelector ('div.rounded.border.bg-muted')).not.toBeNull ()
+    expect (container.textContent).toBe ('')
     expect (screen.queryByRole ('img')).toBeNull ()
   })
 
diff --git a/frontend/src/components/posts/import/PostImportThumbnailPreview.tsx b/frontend/src/components/posts/import/PostImportThumbnailPreview.tsx
index 23bb13d..b692c92 100644
--- a/frontend/src/components/posts/import/PostImportThumbnailPreview.tsx
+++ b/frontend/src/components/posts/import/PostImportThumbnailPreview.tsx
@@ -2,7 +2,6 @@ import { useEffect, useRef, useState } from 'react'
 
 import PostThumbnailPreview from '@/components/posts/PostThumbnailPreview'
 import { apiGet } from '@/lib/api'
-import { cn } from '@/lib/utils'
 
 import type { FC } from 'react'
 
@@ -18,7 +17,6 @@ const PostImportThumbnailPreview: FC<Props> = (
       className = 'h-16 w-16' },
 ) => {
   const [previewUrl, setPreviewUrl] = useState ('')
-  const [unavailable, setUnavailable] = useState (false)
   const previewUrlRef = useRef ('')
 
   useEffect (() => {
@@ -28,7 +26,6 @@ const PostImportThumbnailPreview: FC<Props> = (
         previewUrlRef.current = ''
       }
     setPreviewUrl ('')
-    setUnavailable (false)
 
     if (!(url))
       return
@@ -51,7 +48,7 @@ const PostImportThumbnailPreview: FC<Props> = (
       catch
       {
         if (active)
-          setUnavailable (true)
+          setPreviewUrl ('')
       }
     }
 
@@ -67,20 +64,6 @@ const PostImportThumbnailPreview: FC<Props> = (
     }
   }, [url])
 
-  if (unavailable)
-    {
-      return (
-          <div
-              className={cn (
-                  className,
-                  'flex items-center justify-center rounded border',
-                  'border-amber-300 bg-amber-50 p-2 text-center text-xs',
-                  'text-amber-700 dark:border-amber-900 dark:bg-amber-950',
-                  'dark:text-amber-200')}>
-            サムネールを表示できません
-          </div>)
-    }
-
   return (
       <PostThumbnailPreview
           url={previewUrl}