diff --git a/build/build-report.js b/build/build-report.js
index 2b16c5173de0..5f172b83b3c8 100644
--- a/build/build-report.js
+++ b/build/build-report.js
@@ -90,14 +90,42 @@ async function buildFlowReport() {
 }
 
 async function buildEsModulesBundle() {
+  // Include the type detail for bundle.esm.d.ts generation
+  const i18nModuleShim = `
+/**
+ * Returns a new LHR with all strings changed to the new requestedLocale.
+ * @param {LH.Result} lhr
+ * @param {LH.Locale} requestedLocale
+ * @return {{lhr: LH.Result, missingIcuMessageIds: string[]}}
+ */
+export function swapLocale(lhr, requestedLocale) {
+  // Stub function only included for types
+  return {
+    lhr,
+    missingIcuMessageIds: [],
+  };
+}
+
+/**
+ * Populate the i18n string lookup dict with locale data
+ * Used when the host environment selects the locale and serves lighthouse the intended locale file
+ * @see https://docs.google.com/document/d/1jnt3BqKB-4q3AE94UWFA0Gqspx8Sd_jivlB7gQMlmfk/edit
+ * @param {LH.Locale} locale
+ * @param {Record<string, {message: string}>} lhlMessages
+ */
+function registerLocaleData(locale, lhlMessages) {
+  // Stub function only included for types
+}
+export const format = {registerLocaleData};
+`;
+
   const bundle = await rollup({
     input: 'report/clients/bundle.js',
     plugins: [
       rollupPlugins.commonjs(),
       // Exclude this 30kb from the devtools bundle for now.
       rollupPlugins.shim({
-        [`${LH_ROOT}/shared/localization/i18n-module.js`]:
-            'export const swapLocale = _ => {}; export const format = _ => {};',
+        [`${LH_ROOT}/shared/localization/i18n-module.js`]: i18nModuleShim,
       }),
     ],
   });