diff --git a/Classes/PHPExcel/Writer/Excel5.php b/Classes/PHPExcel/Writer/Excel5.php
index 37f5b85c3..285bdda49 100644
--- a/Classes/PHPExcel/Writer/Excel5.php
+++ b/Classes/PHPExcel/Writer/Excel5.php
@@ -481,7 +481,15 @@ private function _buildWorkbookEscher()
 					case 1: // GIF, not supported by BIFF8, we convert to PNG
 						$blipType = PHPExcel_Shared_Escher_DggContainer_BstoreContainer_BSE::BLIPTYPE_PNG;
 						ob_start();
-						imagepng(imagecreatefromgif($filename));
+						if(extension_loaded('gd'))
+						{
+							imagepng(imagecreatefromgif($filename));
+						}
+						else
+						{
+
+							throw new PHPExcel_Writer_Exception("Failed to create PNG file -- GD is not enabled.");
+						}
 						$blipData = ob_get_contents();
 						ob_end_clean();
 						break;
@@ -499,7 +507,14 @@ private function _buildWorkbookEscher()
 					case 6: // Windows DIB (BMP), we convert to PNG
 						$blipType = PHPExcel_Shared_Escher_DggContainer_BstoreContainer_BSE::BLIPTYPE_PNG;
 						ob_start();
-						imagepng(PHPExcel_Shared_Drawing::imagecreatefrombmp($filename));
+						if(extension_loaded('gd'))
+						{
+							imagepng(PHPExcel_Shared_Drawing::imagecreatefrombmp($filename));
+						}
+						else
+						{
+							throw new PHPExcel_Writer_Exception("Failed to create PNG file -- GD is not enabled.");
+						}
 						$blipData = ob_get_contents();
 						ob_end_clean();
 						break;