diff --git a/PHPExcel/Calculation.php b/PHPExcel/Calculation.php
index 072f69e..fe62d14 100644
--- a/PHPExcel/Calculation.php
+++ b/PHPExcel/Calculation.php
@@ -2955,7 +2955,7 @@ class PHPExcel_Calculation {
 //					echo 'Element is a Variable, Constant, String, Number or Boolean<br />';
 					//	If the last entry on the stack was a : operator, then we may have a row or column range reference
 					$testPrevOp = $stack->last(1);
-					if ($testPrevOp['value'] == ':') {
+					if (isset($testPrevOp['value']) && $testPrevOp['value'] == ':') {
 						$startRowColRef = $output[count($output)-1]['value'];
 						$rangeWS1 = '';
 						if (strpos('!',$startRowColRef) !== FALSE) {
diff --git a/PHPExcel/ReferenceHelper.php b/PHPExcel/ReferenceHelper.php
index 402f2b4..f9fe4dc 100644
--- a/PHPExcel/ReferenceHelper.php
+++ b/PHPExcel/ReferenceHelper.php
@@ -889,9 +889,9 @@ class PHPExcel_ReferenceHelper
 			list($newColumn, $newRow) = PHPExcel_Cell::coordinateFromString( $pCellReference );
 
 			// Verify which parts should be updated
-			$updateColumn = (($newColumn{0} != '$') && ($beforeColumn{0} != '$') &&
+			$updateColumn = (($newColumn[0] != '$') && ($beforeColumn[0] != '$') &&
 							 PHPExcel_Cell::columnIndexFromString($newColumn) >= PHPExcel_Cell::columnIndexFromString($beforeColumn));
-			$updateRow = (($newRow{0} != '$') && ($beforeRow{0} != '$') &&
+			$updateRow = (($newRow[0] != '$') && ($beforeRow[0] != '$') &&
 						  $newRow >= $beforeRow);
 
 			// Create new column reference