diff --git a/Classes/PHPExcel/Writer/HTML.php b/Classes/PHPExcel/Writer/HTML.php
index 762ed23..46adb2e 100644
--- a/Classes/PHPExcel/Writer/HTML.php
+++ b/Classes/PHPExcel/Writer/HTML.php
@@ -639,7 +639,7 @@ class PHPExcel_Writer_HTML extends PHPExcel_Writer_Abstract implements PHPExcel_
 			    $chartCoordinates = $chart->getTopLeftPosition();
 				if ($chartCoordinates['cell'] == $coordinates) {
 //					$chartFileName = tempnam(PHPExcel_Shared_File::sys_get_temp_dir(),'xlc');
-					$chartFileName = './'.uniqid().'.png';
+					$chartFileName = PHPExcel_Shared_File::sys_get_temp_dir().'/'.uniqid().'.png';
 					if (!$chart->render($chartFileName)) {
 						return;
 					}