diff --git a/Classes/PHPExcel/Calculation.php b/Classes/PHPExcel/Calculation.php
index b844b1ff..b12c960a 100644
--- a/Classes/PHPExcel/Calculation.php
+++ b/Classes/PHPExcel/Calculation.php
@@ -3193,6 +3193,11 @@ class PHPExcel_Calculation {
 						$cellRef = $matches[6].$matches[7].':'.$matches[9].$matches[10];
 						if ($matches[2] > '') {
 							$matches[2] = trim($matches[2],"\"'");
+							if ((strpos($matches[2],'[') !== false) || (strpos($matches[2],']') !== false)) {
+								//	It's a Reference to an external workbook (not currently supported)
+								return $this->_raiseFormulaError('Unable to access External Workbook');
+							}
+							$matches[2] = trim($matches[2],"\"'");
 //							echo '$cellRef='.$cellRef.' in worksheet '.$matches[2].'<br />';
 							$this->_writeDebug('Evaluating Cell Range '.$cellRef.' in worksheet '.$matches[2]);
 							if (!is_null($pCellParent)) {
@@ -3222,6 +3227,10 @@ class PHPExcel_Calculation {
 						$cellRef = $matches[6].$matches[7];
 						if ($matches[2] > '') {
 							$matches[2] = trim($matches[2],"\"'");
+							if ((strpos($matches[2],'[') !== false) || (strpos($matches[2],']') !== false)) {
+								//	It's a Reference to an external workbook (not currently supported)
+								return $this->_raiseFormulaError('Unable to access External Workbook');
+							}
 //							echo '$cellRef='.$cellRef.' in worksheet '.$matches[2].'<br />';
 							$this->_writeDebug('Evaluating Cell '.$cellRef.' in worksheet '.$matches[2]);
 							if (!is_null($pCellParent)) {
diff --git a/changelog.txt b/changelog.txt
index cbacf025..772db20f 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -41,6 +41,7 @@ Fixed in SVN:
 - Bugfix:   (MBaker) Work item 16212 - $arguments improperly used in CachedObjectStorage/PHPTemp.php
 - Bugfix:   (MBaker) Work item 16643 - Bug In Cache System (cell reference when throwing caching errors)
 - Bugfix:   (MBaker) Work item 16895 - PHP Invalid index notice on writing excel file when active sheet has been deleted
+- Bugfix:   (MBaker) Work item 16956 - External links in Excel2010 files cause Fatal error
 - General:  (MBaker) Work item 15405 - Two easy to fix Issues concerning PHPExcel_Token_Stack (l10n/UC)
 - General:  (MBaker) Work item 15461 - Locale file paths not fit for windows
 - General:  (MBaker) Work item 16643 - Add file directory as a cache option for cache_to_discISAM