diff --git a/src/components/MarkdownContent.tsx b/src/components/MarkdownContent.tsx
index 72c84461..056b8da2 100644
--- a/src/components/MarkdownContent.tsx
+++ b/src/components/MarkdownContent.tsx
@@ -3,9 +3,10 @@ import Markdown, { defaultUrlTransform } from 'react-markdown'
 import remarkGfm from 'remark-gfm'
 import rehypeHighlight from 'rehype-highlight'
 import { preprocessWikilinks, WIKILINK_SCHEME } from '../utils/chatWikilinks'
+import { supportsModernRegexFeatures } from '../utils/regexCapabilities'
 
 const REMARK_PLUGINS = [remarkGfm]
-const REHYPE_PLUGINS = [rehypeHighlight]
+const REHYPE_PLUGINS = supportsModernRegexFeatures() ? [rehypeHighlight] : []
 
 function wikilinkUrlTransform(url: string): string {
   if (url.startsWith(WIKILINK_SCHEME)) return url
diff --git a/src/components/MarkdownContent.webkit.test.tsx b/src/components/MarkdownContent.webkit.test.tsx
new file mode 100644
index 00000000..d0a64f69
--- /dev/null
+++ b/src/components/MarkdownContent.webkit.test.tsx
@@ -0,0 +1,60 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { render, screen } from '@testing-library/react'
+
+const nativeRegExpDescriptor = Object.getOwnPropertyDescriptor(globalThis, 'RegExp')
+const NativeRegExp = RegExp
+
+function setRegExpConstructor(value: RegExpConstructor) {
+  Object.defineProperty(globalThis, 'RegExp', {
+    configurable: true,
+    writable: true,
+    value,
+  })
+}
+
+function restoreRegExpConstructor() {
+  if (nativeRegExpDescriptor) {
+    Object.defineProperty(globalThis, 'RegExp', nativeRegExpDescriptor)
+  }
+}
+
+function rejectsLegacyWebKitRegex(source: string, flags?: string): boolean {
+  if (flags?.includes('d')) return true
+  if (flags?.includes('v')) return true
+  return source.includes('(?<')
+}
+
+function installLegacyWebKitRegExp() {
+  const LegacyWebKitRegExp = function (pattern?: string | RegExp, flags?: string) {
+    const source = pattern instanceof NativeRegExp ? pattern.source : String(pattern ?? '')
+    if (rejectsLegacyWebKitRegex(source, flags)) {
+      throw new SyntaxError('Invalid regular expression: invalid group specifier name')
+    }
+
+    return new NativeRegExp(pattern, flags)
+  } as RegExpConstructor
+
+  Object.setPrototypeOf(LegacyWebKitRegExp, NativeRegExp)
+  LegacyWebKitRegExp.prototype = NativeRegExp.prototype
+
+  setRegExpConstructor(LegacyWebKitRegExp)
+}
+
+afterEach(() => {
+  restoreRegExpConstructor()
+  vi.resetModules()
+})
+
+describe('MarkdownContent WebKit regex fallback', () => {
+  it('renders AI code fences without syntax highlighting when modern regex features are unavailable', async () => {
+    installLegacyWebKitRegExp()
+    vi.resetModules()
+
+    const { MarkdownContent } = await import('./MarkdownContent')
+
+    expect(() => {
+      render(<MarkdownContent content={'```ts\nconst prompt = "(?<name>.*)"\n```'} />)
+    }).not.toThrow()
+    expect(screen.getByText('const prompt = "(?<name>.*)"')).toBeInTheDocument()
+  })
+})
diff --git a/src/components/codeBlockOptions.ts b/src/components/codeBlockOptions.ts
index 282b4e77..271b6f82 100644
--- a/src/components/codeBlockOptions.ts
+++ b/src/components/codeBlockOptions.ts
@@ -1,21 +1,12 @@
 import { codeBlockOptions } from '@blocknote/code-block'
 import type { CodeBlockOptions } from '@blocknote/core'
+import { supportsModernRegexFeatures } from '../utils/regexCapabilities'
 
 const LIGHT_CODE_THEME = 'github-light'
 const DARK_CODE_THEME = 'github-dark'
 
 type TolariaCodeHighlighter = Awaited<ReturnType<NonNullable<typeof codeBlockOptions.createHighlighter>>>
 
-function supportsShikiPrecompiledRegexFlags() {
-  try {
-    new RegExp('', 'd')
-    new RegExp('[[]]', 'v')
-    return true
-  } catch {
-    return false
-  }
-}
-
 function currentCodeBlockTheme() {
   if (typeof document === 'undefined') return LIGHT_CODE_THEME
 
@@ -44,7 +35,7 @@ export function createTolariaCodeBlockOptions(): Partial<CodeBlockOptions> {
     defaultLanguage: 'text',
   }
 
-  if (supportsShikiPrecompiledRegexFlags()) return options
+  if (supportsModernRegexFeatures()) return options
 
   delete options.createHighlighter
   return options
diff --git a/src/components/editorSchema.webkit.test.ts b/src/components/editorSchema.webkit.test.ts
index 6b0a7255..da43fc2a 100644
--- a/src/components/editorSchema.webkit.test.ts
+++ b/src/components/editorSchema.webkit.test.ts
@@ -17,10 +17,10 @@ function restoreRegExpConstructor() {
   }
 }
 
-function installLegacyWebKitRegExp() {
+function installMockRegExp(shouldReject: (pattern: string | RegExp | undefined, flags: string | undefined) => boolean) {
   const LegacyWebKitRegExp = function (pattern?: string | RegExp, flags?: string) {
-    if (flags?.includes('d') || flags?.includes('v')) {
-      throw new SyntaxError('Invalid flags supplied to RegExp constructor')
+    if (shouldReject(pattern, flags)) {
+      throw new SyntaxError('Invalid regular expression: invalid group specifier name')
     }
 
     return new NativeRegExp(pattern, flags)
@@ -32,6 +32,14 @@ function installLegacyWebKitRegExp() {
   setRegExpConstructor(LegacyWebKitRegExp)
 }
 
+function installLegacyWebKitRegExp() {
+  installMockRegExp((_pattern, flags) => Boolean(flags?.includes('d') || flags?.includes('v')))
+}
+
+function installLookbehindMissingRegExp() {
+  installMockRegExp((pattern) => typeof pattern === 'string' && pattern.includes('(?<'))
+}
+
 afterEach(() => {
   document.documentElement.classList.remove('dark')
   delete document.documentElement.dataset.theme
@@ -70,4 +78,13 @@ describe('editor schema code block highlighting', () => {
 
     expect(createTolariaCodeBlockOptions()).not.toHaveProperty('createHighlighter')
   })
+
+  it('omits the Shiki highlighter when WebKit lacks regex lookbehind syntax', async () => {
+    installLookbehindMissingRegExp()
+    vi.resetModules()
+
+    const { createTolariaCodeBlockOptions } = await import('./codeBlockOptions')
+
+    expect(createTolariaCodeBlockOptions()).not.toHaveProperty('createHighlighter')
+  })
 })
diff --git a/src/utils/regexCapabilities.ts b/src/utils/regexCapabilities.ts
new file mode 100644
index 00000000..99215d91
--- /dev/null
+++ b/src/utils/regexCapabilities.ts
@@ -0,0 +1,12 @@
+export function supportsModernRegexFeatures(): boolean {
+  try {
+    new RegExp('', 'd')
+    new RegExp('[[]]', 'v')
+    new RegExp('(?<=a)b')
+    new RegExp('(?<!a)b')
+    new RegExp('(?<label>a)')
+    return true
+  } catch {
+    return false
+  }
+}