diff --git a/lti_util/OAuth.php b/lti_util/OAuth.php
index a5490b0161e61eac98e09161596579c6d44cb33b..8ad89a49b7addf19588c7166e08a40677f055e3a 100644
--- a/lti_util/OAuth.php
+++ b/lti_util/OAuth.php
@@ -12,6 +12,7 @@ class OAuthException extends Exception {
 class OAuthConsumer {
   public $key;
   public $secret;
+  public $callback_url;
 
   function __construct($key, $secret, $callback_url=NULL) {
     $this->key = $key;