diff --git a/Classes/PHPExcel/CachedObjectStorage/DiscISAM.php b/Classes/PHPExcel/CachedObjectStorage/DiscISAM.php
index 3087680e..327f4b4e 100644
--- a/Classes/PHPExcel/CachedObjectStorage/DiscISAM.php
+++ b/Classes/PHPExcel/CachedObjectStorage/DiscISAM.php
@@ -112,7 +112,7 @@ class PHPExcel_CachedObjectStorage_DiscISAM extends PHPExcel_CachedObjectStorage
 		parent::copyCellCollection($parent);
 		//	Get a new id for the new file name
 		$baseUnique = $this->_getUniqueID();
-		$newFileName = sys_get_temp_dir().'/PHPExcel.'.$baseUnique.'.cache';
+		$newFileName = PHPExcel_Shared_File::sys_get_temp_dir().'/PHPExcel.'.$baseUnique.'.cache';
 		//	Copy the existing cell cache file
 		copy ($this->_fileName,$newFileName);
 		$this->_fileName = $newFileName;
@@ -140,7 +140,7 @@ class PHPExcel_CachedObjectStorage_DiscISAM extends PHPExcel_CachedObjectStorage
 		parent::__construct($parent);
 		if (is_null($this->_fileHandle)) {
 			$baseUnique = $this->_getUniqueID();
-			$this->_fileName = sys_get_temp_dir().'/PHPExcel.'.$baseUnique.'.cache';
+			$this->_fileName = PHPExcel_Shared_File::sys_get_temp_dir().'/PHPExcel.'.$baseUnique.'.cache';
 			$this->_fileHandle = fopen($this->_fileName,'a+');
 		}
 	}	//	function __construct()
diff --git a/changelog.txt b/changelog.txt
index 054ae6f4..252cb27f 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -60,6 +60,7 @@ Fixed in SVN:
 - Bugfix:	(MBaker) Work item 15121 - Column reference rather than cell reference in Print Area definition
 						Fix Excel2007 Writer to handle print areas that are defined as row or column ranges rather than just as cell ranges
 - Bugfix:	(MBaker) Reduced false positives from isDateTimeFormatCode() method by suppressing testing within quoted strings
+- Bugfix:	(MBaker) Work item 15312 - Caching and tmp partition exhaustion 
 - General:  (MBaker) Improved performance (speed), for building the Shared Strings table in the Excel2007 Writer.
 - General:  (MBaker) Enhanced SheetViews element structures in the Excel2007 Writer for frozen panes.