diff --git a/lib/Auth/OAuth.php b/lib/Auth/OAuth.php
index fc963560..1ea8ca9a 100755
--- a/lib/Auth/OAuth.php
+++ b/lib/Auth/OAuth.php
@@ -522,7 +522,7 @@ protected function getQueryParameters($isPost, $parameters)
      */
     protected function isOauth1()
     {
-        return strlen($this->_request_token_url) > 0;
+        return !empty($this->_request_token_url) && strlen($this->_request_token_url) > 0;
     }
 
     /**