--- geshifilter.module.orig	2011-10-11 20:30:28.000000000 +1100
+++ geshifilter.module	2011-10-11 20:30:54.000000000 +1100
@@ -316,7 +316,7 @@
  */
 function geshifilter_generate_language_css_rules() {
   require_once drupal_get_path('module', 'geshifilter') .'/geshifilter.admin.inc';
-  drupal_set_header("Content-type: text/css");
+  drupal_add_http_header("Content-type", "text/css");
   $output = _geshifilter_generate_languages_css_rules();
   print($output);
   exit();