diff --git a/internal/check-locale-reachable.mjs b/internal/check-locale-reachable.mjs
index e0d777eb9..ab2a18bf6 100644
--- a/internal/check-locale-reachable.mjs
+++ b/internal/check-locale-reachable.mjs
@@ -31,9 +31,40 @@ const SUPPORTED = (src.match(/SUPPORTED_LOCALES = \[([^\]]*)\]/) || [])[1]
 
 // Evaluate the SHIPPED detectLocale rather than reimplementing it — a gate that
 // reimplements the thing it tests only ever proves the copy agrees with itself.
-const body = src.slice(src.indexOf('export function detectLocale'), src.indexOf('export function createAppI18n'))
+// ★ TAKE THE FUNCTION, NOT THE GAP BETWEEN TWO LANDMARKS.
+// This used to slice from `export function detectLocale` to `export function createAppI18n` and eval
+// whatever lay between. That is a promise about the ORDER OF A FILE the gate does not own: the day
+// someone exported a helper between those two lines, the slice carried a bare `export` into
+// new Function() and this gate died with "Unexpected token 'export'" — twice, once for a helper I
+// added myself. It was then "fixed" by moving the helper, which only re-armed the trap for the next
+// person. Extract detectLocale by matching its own braces, and strip any export keyword that
+// survives, so the gate reads the function it names and nothing else.
+function extractFunction(source, name) {
+  const start = source.search(new RegExp('(export\\s+)?function\\s+' + name + '\\s*\\('))
+  if (start < 0) return ''
+  const open = source.indexOf('{', start)
+  if (open < 0) return ''
+  let depth = 0
+  for (let i = open; i < source.length; i++) {
+    const ch = source[i]
+    if (ch === '{') depth++
+    else if (ch === '}') {
+      depth--
+      if (depth === 0) return source.slice(start, i + 1)
+    }
+  }
+  return ''
+}
+const body = extractFunction(src, 'detectLocale').replace(/\bexport\s+/g, '')
+if (!body) {
+  console.error('LOCALE-REACHABLE: FAIL — could not find detectLocale() in library/i18n/index.js.')
+  console.error('  The gate evaluates the SHIPPED function rather than reimplementing it, so if the')
+  console.error('  function is renamed this must be updated — silence here would be a gate that')
+  console.error('  stopped testing anything.')
+  process.exit(1)
+}
 const make = new Function('SUPPORTED_LOCALES', 'window', 'document',
-  `${body.replace('export function', 'return function')}\n; return detectLocale;`)
+  `${body}\n; return detectLocale;`)
 const detect = (search, htmlLang) =>
   make(SUPPORTED, { location: { search } }, { documentElement: { lang: htmlLang } })()