diff --git a/lib/modules/auth/index.js b/lib/modules/auth/index.js
index 5b58a40c..c6db2f6d 100644
--- a/lib/modules/auth/index.js
+++ b/lib/modules/auth/index.js
@@ -160,7 +160,7 @@ export default class Auth extends Base {
    * Returns a list of authentication providers that can be used to sign in a given user (identified by its main email address).
    * @return {Promise}
    */
-  fetchProvidersForEmail(email: string): Promise<Object> {
+  fetchProvidersForEmail(email: string): Promise<Array<String>> {
     return FirebaseAuth.fetchProvidersForEmail(email);
   }