diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index e28c23a..f1d65a3 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -452,7 +452,7 @@
 	 */
 	public function set_alt_message($str = '')
 	{
-		$this->alt_message = $str;
+		$this->alt_message = (string) $str;
 		return $this;
 	}