diff --git a/mail/inc/class.mail_ui.inc.php b/mail/inc/class.mail_ui.inc.php
index a235c3aca2..11417cc653 100644
--- a/mail/inc/class.mail_ui.inc.php
+++ b/mail/inc/class.mail_ui.inc.php
@@ -1967,7 +1967,7 @@ class mail_ui
 
 		$preventRedirect=false;
 		if(isset($_requesteddata['id'])) $rowID	= $_requesteddata['id'];
-		if(isset($_requesteddata['part'])) $partID = $_requesteddata['part'];
+		if(isset($_requesteddata['part'])) $partID = $_requesteddata['part']!='null'?$_requesteddata['part']:null;
 		if(isset($_requesteddata['mode'])) $preventRedirect   = (($_requesteddata['mode']=='display' || $_requesteddata['mode'] == 'print')?true:false);
 
 		$hA = self::splitRowID($rowID);
diff --git a/mail/js/app.js b/mail/js/app.js
index 7a6a762f68..12333abfa3 100644
--- a/mail/js/app.js
+++ b/mail/js/app.js
@@ -2239,7 +2239,8 @@ app.classes.mail = AppJS.extend(
 			attgrid = this.et2.getArrayMgr("content").getEntry('attachments')[widget.id.replace(/\[name\]/,'')];
 			var mailids = this.et2.getArrayMgr("content").getEntry('processedmail_id');
 			var mailida = mailids.split(',');
-			mailid = mailida[widget.id.replace(/\[name\]/,'')];
+			// either several attachments of one email, or multiple emlfiles
+			mailid = mailida.length==1 ? mailida[0] : mailida[widget.id.replace(/\[name\]/,'')];
 			if (typeof attgrid.uid != 'undefined' && attgrid.uid && mailid.indexOf(attgrid.uid)==-1)
 			{
 				for (var i=0; i<mailida.length; i++)