diff --git a/src/backend/index.ts b/src/backend/index.ts
index 69a5fce..ee7e125 100644
--- a/src/backend/index.ts
+++ b/src/backend/index.ts
@@ -27,3 +27,5 @@ export function createPublicKeyAuthenticator(opts: CreateAuthenticatorOptions):
         get: get.bind(undefined, opts),
     }
 }
+
+export { isRegistrableDomain } from './util'