diff --git a/Classes/PHPExcel/Writer/Excel5/Workbook.php b/Classes/PHPExcel/Writer/Excel5/Workbook.php
index 0e0bbda5..f8599d58 100644
--- a/Classes/PHPExcel/Writer/Excel5/Workbook.php
+++ b/Classes/PHPExcel/Writer/Excel5/Workbook.php
@@ -536,7 +536,7 @@ class PHPExcel_Writer_Excel5_Workbook extends PHPExcel_Writer_Excel5_BIFFwriter
 
 		// Create EXTERNSHEET for each worksheet
 		for ($i = 0; $i < $countSheets; ++$i) {
-			$this->_writeExternsheet($phpExcel->getSheet($i)->getTitle());
+			$this->_writeExternsheet($this->_phpExcel->getSheet($i)->getTitle());
 		}
 	}