diff --git a/frontend/src/components/DraggableDroppableTagRow.test.tsx b/frontend/src/components/DraggableDroppableTagRow.test.tsx
index 43a32aa..cdddba6 100644
--- a/frontend/src/components/DraggableDroppableTagRow.test.tsx
+++ b/frontend/src/components/DraggableDroppableTagRow.test.tsx
@@ -1,9 +1,25 @@
+import { screen } from '@testing-library/react'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import DraggableDroppableTagRow from '@/components/DraggableDroppableTagRow'
 import { buildTag } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
 
+import type { CSSProperties, ReactNode } from 'react'
+
+vi.mock ('framer-motion', async importOriginal => {
+  const original = await importOriginal<typeof import ('framer-motion')> ()
+  return {
+      ...original,
+      motion: {
+	  ...original.motion,
+	  div: ({ children, style, layoutId }: {
+	      children?: ReactNode
+	      style?: CSSProperties
+	      layoutId?: string }) => (
+	      <div style={style} data-layout-id={layoutId}>{children}</div>) } }
+})
+
 const dndKit = vi.hoisted (() => ({
   useDraggable: vi.fn (),
   useDroppable: vi.fn (),
@@ -97,4 +113,32 @@ describe ('DraggableDroppableTagRow', () => {
 	}),
     )
   })
+
+  it.each ([false, true]) (
+      'separates same-id internal and external animation identities (sp=%s)',
+      sp => {
+	const internal = buildTag ({ id: 7, name: 'internal_collision' })
+	const external = buildTag ({
+	    id: 7, name: 'nico:external_collision', category: 'nico' })
+
+	renderWithProviders (
+	    <>
+	      {[internal, external].map (item => (
+		  <DraggableDroppableTagRow
+		      key={item.category}
+		      tag={item}
+		      nestLevel={0}
+		      pathKey={`cat-${ item.category }-7`}
+		      suppressClickRef={{ current: false }}
+		      sp={sp}/>))}
+	    </>)
+
+	const prefix = sp ? 'tag-sp-' : 'tag-'
+	for (const item of [internal, external])
+	{
+	  expect (screen.getByRole ('link', { name: item.name })
+	      .closest ('[data-layout-id]')).toHaveAttribute (
+		  'data-layout-id', `${ prefix }${ item.category }-7`)
+	}
+      })
 })
diff --git a/frontend/src/components/DraggableDroppableTagRow.tsx b/frontend/src/components/DraggableDroppableTagRow.tsx
index 7c74006..4cc2751 100644
--- a/frontend/src/components/DraggableDroppableTagRow.tsx
+++ b/frontend/src/components/DraggableDroppableTagRow.tsx
@@ -137,7 +137,7 @@ const DraggableDroppableTagRow: FC<Props> = ({
 		transition={{ layout: layoutTransition }}
 		layoutId={animationMode === 'off'
 		    ? undefined
-		    : `tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
+		    : `tag-${ sp ? 'sp-' : '' }${ tag.category }-${ tag.id }`}>
 	      <TagLink tag={tag} nestLevel={nestLevel}/>
 	    </motion.div>)}
       </div>)
diff --git a/frontend/src/components/TagSidebar.test.tsx b/frontend/src/components/TagSidebar.test.tsx
new file mode 100644
index 0000000..809c354
--- /dev/null
+++ b/frontend/src/components/TagSidebar.test.tsx
@@ -0,0 +1,47 @@
+import { screen } from '@testing-library/react'
+import { describe, expect, it, vi } from 'vitest'
+
+import TagSidebar from '@/components/TagSidebar'
+import { buildPost, buildTag } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+import type { ReactNode } from 'react'
+
+vi.mock ('@/components/TagSearch', () => ({ default: () => null }))
+vi.mock ('@/components/layout/SidebarComponent', () => ({
+    default: ({ children }: { children: ReactNode }) => <>{children}</> }))
+
+vi.mock ('framer-motion', async importOriginal => {
+  const original = await importOriginal<typeof import ('framer-motion')> ()
+  return {
+      ...original,
+      motion: {
+	  ...original.motion,
+	  div: ({ children, layoutId }: {
+	      children?: ReactNode
+	      layoutId?: string }) => (
+	      <div data-layout-id={layoutId}>{children}</div>) } }
+})
+
+describe ('TagSidebar', () => {
+  it ('keeps same-id internal and external tags with distinct identities', () => {
+    const errors = vi.spyOn (console, 'error').mockImplementation (() => {})
+    const internal = buildTag ({ id: 7, name: 'internal_collision' })
+    const external = buildTag ({
+	id: 7, name: 'nico:external_collision', category: 'nico' })
+
+    renderWithProviders (
+	<TagSidebar posts={[buildPost ({ tags: [internal, external] })]}/>)
+
+    for (const item of [internal, external])
+    {
+      const link = screen.getByRole ('link', { name: item.name })
+      expect (link).toBeInTheDocument ()
+      expect (link.closest ('[data-layout-id]')).toHaveAttribute (
+	  'data-layout-id', `tag-${ item.category }-7`)
+    }
+
+    expect (errors.mock.calls.filter (args =>
+	args.some (value => String (value).includes ('same key')))).toEqual ([])
+  })
+})
diff --git a/frontend/src/components/TagSidebar.tsx b/frontend/src/components/TagSidebar.tsx
index 26f21ab..8344881 100644
--- a/frontend/src/components/TagSidebar.tsx
+++ b/frontend/src/components/TagSidebar.tsx
@@ -84,7 +84,8 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
 	<ul>
 	  {CATEGORIES.flatMap (cat => cat in tags ? (
 	      tags[cat].map (tag => (
-		  <li key={tag.id} className="mb-1 min-w-0 max-w-full overflow-hidden">
+		  <li key={`${ cat }-${ tag.id }`}
+		      className="mb-1 min-w-0 max-w-full overflow-hidden">
 		    {animationsOff
 		     ? (
 			 <div className="flex min-w-0 max-w-full items-baseline overflow-hidden">
@@ -94,7 +95,7 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
 			 <motion.div
 			     className="flex min-w-0 max-w-full items-baseline overflow-hidden"
 			     transition={{ layout: layoutTransition }}
-			     layoutId={`tag-${ tag.id }`}>
+			     layoutId={`tag-${ cat }-${ tag.id }`}>
 			   <TagLink tag={tag} onClick={onClick}/>
 			 </motion.div>)}
 		  </li>))) : [])}