diff --git a/inc/3rdparty/libraries/PHPePub/Zip.php b/inc/3rdparty/libraries/PHPePub/Zip.php
index 01e035662..92e78e703 100644
--- a/inc/3rdparty/libraries/PHPePub/Zip.php
+++ b/inc/3rdparty/libraries/PHPePub/Zip.php
@@ -569,7 +569,7 @@ class Zip {
                 if ($inline) {
                     $cd .= "inline";
 				} else{
-                    $cd .= "attached";
+                    $cd .= "attachment";
 				}
                 if ($fileName) {
                     $cd .= '; filename="' . $fileName . '"';