diff --git a/lib/Moip.php b/lib/Moip.php
index 08f1bef..9cc8e52 100644
--- a/lib/Moip.php
+++ b/lib/Moip.php
@@ -494,7 +494,7 @@ public function addMessage($msg) {
      */
     public function setReturnURL($url) {
         if (!isset($this->xml->InstrucaoUnica->URLRetorno)) {
-            $this->xml->InstrucaoUnica->addChild('URLRetorno', $url);
+            $this->xml->InstrucaoUnica->URLRetorno = $url;
         }
 		return $this;
     }
@@ -509,7 +509,7 @@ public function setReturnURL($url) {
      */
     public function setNotificationURL($url) {
         if (!isset($this->xml->InstrucaoUnica->URLNotificacao)) {
-            $this->xml->InstrucaoUnica->addChild('URLNotificacao', $url);
+            $this->xml->InstrucaoUnica->URLNotificacao = $url;
         }
     }
 
@@ -814,4 +814,4 @@ function __construct($base_url = '', $name = '')
 		$this->base_url = $base_url;
 		$this->name = $name;
 	}
-}
\ No newline at end of file
+}