diff --git a/src/Storage/Mbox.php b/src/Storage/Mbox.php
index a841382a..accf0fff 100644
--- a/src/Storage/Mbox.php
+++ b/src/Storage/Mbox.php
@@ -199,7 +199,7 @@ public function __construct($params)
         }
 
         if (isset($params->messageEOL)) {
-            $this->messageEOL = $params->messageEOL;
+            $this->messageEOL = (string) $params->messageEOL;
         }
 
         $this->openMboxFile($params->filename);