diff --git a/main/inc/lib/pdf.lib.php b/main/inc/lib/pdf.lib.php
index 4d69a1613f..77bb829572 100644
--- a/main/inc/lib/pdf.lib.php
+++ b/main/inc/lib/pdf.lib.php
@@ -220,7 +220,7 @@ class PDF {
         
         //absolute path for frames.css //TODO: necessary?
         $absolute_css_path 	= api_get_path(WEB_CODE_PATH).'css/'.api_get_setting('stylesheets').'/frames.css';
-        $document_html		= str_replace('href="./css/frames.css"',$absolute_css_path, $document_html);
+        $document_html		= str_replace('href="./css/frames.css"','href="'.$absolute_css_path.'"', $document_html);
         
         //$document_html=str_replace('<link rel="stylesheet" http://my.chamilo.net/main/css/chamilo/frames.css type="text/css" />','', $document_html);