Index: core/ViewDataTable/GenerateGraphHTML.php
===================================================================
--- core/ViewDataTable/GenerateGraphHTML.php	(revision 1393)
+++ core/ViewDataTable/GenerateGraphHTML.php	(working copy)
@@ -135,7 +135,7 @@
 					image: function (src) { return "<img title=\'Piwik Graph\' src=\'data:image/png;base64," + $("#"+src)[0].get_img_binary() + "\' />"; },
 					popup: function (src) {
 						var img_win = window.open("", "ExportChartAsImage");
-						img_win.document.write("<html><head><title>'. Piwik_Translate('General_ExportAsImage') .'<\/title><\/head><body>" + Control.OFC.image(src) + "<br><br><p>'. htmlentities(Piwik_Translate('General_SaveImageOnYourComputer')) .'<\/p><\/body><\/html>");
+						img_win.document.write("<!DOCTYPE HTML PUBLIC \"-\/\/W3C//DTD XHTML 1.0 Transitional\/\/EN\" \"http:\/\/www.w3.org\/TR\/xhtml1\/DTD\/xhtml1-transitional.dtd\" /><html xmlns=\"http:\/\/www.w3.org\/1999\/xhtml\"><head><meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\" \/><title>'. Piwik_Translate('General_ExportAsImage') .'<\/title><\/head><body>" + Control.OFC.image(src) + "<br \/><br \/><p>'. htmlentities(Piwik_Translate('General_SaveImageOnYourComputer')) .'<\/p><\/body><\/html>");
 					}
 				};
 				if (typeof Control == "undefined") { var Control = {OFC: OFC.jquery}; }
