diff --git a/src/directive.js b/src/directive.js
index bab7968..53994f2 100644
--- a/src/directive.js
+++ b/src/directive.js
@@ -16,7 +16,7 @@
             scope: {
                 response: '=?ngModel',
                 key: '=',
-                theme: '?=',
+                theme: '=?',
                 onCreate: '&',
                 onSuccess: '&',
                 onExpire: '&'