diff --git a/Classes/PHPExcel/Style/NumberFormat.php b/Classes/PHPExcel/Style/NumberFormat.php
index ed6ace9..dde1ad9 100644
--- a/Classes/PHPExcel/Style/NumberFormat.php
+++ b/Classes/PHPExcel/Style/NumberFormat.php
@@ -439,7 +439,7 @@ class PHPExcel_Style_NumberFormat extends PHPExcel_Style_Supervisor implements P
 	 * @param array		$callBack	Callback function for additional formatting of string
 	 * @return string	Formatted string
 	 */
-	public static function toFormattedString($value = '', $format = '', $callBack = null)
+	public static function toFormattedString($value = PHPExcel_Style_NumberFormat::FORMAT_GENERAL, $format = '', $callBack = null)
 	{
 		// For now we do not treat strings although section 4 of a format code affects strings
 		if (!is_numeric($value)) return $value;
diff --git a/Classes/PHPExcel/Worksheet.php b/Classes/PHPExcel/Worksheet.php
index 9e65256..9791ead 100644
--- a/Classes/PHPExcel/Worksheet.php
+++ b/Classes/PHPExcel/Worksheet.php
@@ -2432,7 +2432,10 @@ class PHPExcel_Worksheet implements PHPExcel_IComparable
                         if ($formatData) {
                             $style = $this->_parent->getCellXfByIndex($cell->getXfIndex());
                             $returnValue[$rRef][$cRef] = PHPExcel_Style_NumberFormat::toFormattedString(
-                            	$returnValue[$rRef][$cRef], $style->getNumberFormat()->getFormatCode()
+                            	$returnValue[$rRef][$cRef], 
+								($style->getNumberFormat()) ? 
+									$style->getNumberFormat()->getFormatCode() : 
+									PHPExcel_Style_NumberFormat::FORMAT_GENERAL
                             );
                         }
                     } else {
diff --git a/changelog.txt b/changelog.txt
index a1a6a23..b626123 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -53,6 +53,7 @@ Fixed in develop branch for release v1.7.9:
 - Feature:  (Progi1984) Work item GH-8/CP11704 : Conditional formatting in Excel 5 Writer
 - Bugfix:   (MBaker)    Work item GH-113 - canRead() Error for GoogleDocs ODS files: in ODS files from Google Docs there is no mimetype file
 - Bugfix:   (MBaker)    Work item GH-80  - "Sheet index is out of bounds." Exception
+- Bugfix:   (ccorliss)  Work item GH-105 - Fixed number format fatal error
 
 --------------------------------------------------------------------------------
 BREAKING CHANGE! As part of the planned changes for handling array formulae in