diff --git a/Services/IMSProvider.php b/Services/IMSProvider.php
index 74a393b..63ebc8c 100644
--- a/Services/IMSProvider.php
+++ b/Services/IMSProvider.php
@@ -46,7 +46,7 @@ public function prepareLaunchRequest(array $extraParameters = array())
     {
         $parameters = array_merge($this->parameters, $extraParameters);
 
-        $oauthRequest = new OauthRequest($parameters, $this->config['url'], $this->config['baseUrl'], $this->config['key'], $this->config['secret']);
+        $oauthRequest = new OauthRequest($parameters, $this->config['url'], $this->config['base_url'], $this->config['key'], $this->config['secret']);
         $oauthRequest->signRequest();
 
         return $oauthRequest;
@@ -75,6 +75,7 @@ public function configureOptions(OptionsResolver $resolver)
             'secret',
             'key',
             'url',
+            'base_url'
         ));
     }
 }