diff --git a/src/shared.ts b/src/shared.ts
index 70bf362..3f0837a 100644
--- a/src/shared.ts
+++ b/src/shared.ts
@@ -42,8 +42,7 @@ export function toLocale(val: string | Intl.Locale): Intl.Locale {
  */
 export function validateLangTag(lang: string): boolean {
   try {
-    // TODO: if we have a better way to validate the language tag, we should use it.
-    new Intl.Locale(lang)
+    Intl.getCanonicalLocales(lang)
     return true
   } catch {
     return false
diff --git a/src/shim.d.ts b/src/shim.d.ts
new file mode 100644
index 0000000..4f541fa
--- /dev/null
+++ b/src/shim.d.ts
@@ -0,0 +1,3 @@
+declare namespace Intl {
+  function getCanonicalLocales(locales: string | string[]): string[]
+}