--- a/pisg/modules/Pisg/HTMLGenerator.pm
+++ b/pisg/modules/Pisg/HTMLGenerator.pm
@@ -242,7 +242,7 @@
     if($self->{cfg}->{colorscheme} ne "none") {
         _html( <<HTML );
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
-<html>
+<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=$self->{cfg}->{charset}" />
 <title>$title</title>