diff --git a/htmltidy.module b/htmltidy.module
index fadcef5..13a92df 100644
--- a/htmltidy.module
+++ b/htmltidy.module
@@ -192,7 +192,7 @@ function htmltidy_string($text, $input, $settings, &$errors, &$warnings) {
   if ($settings['debug']['warnings'] && user_access('use htmltidy debug mode')) {
     $header = "<style type=\"text/css\"> .htmltidy { border: 1px dashed #aaa; background-color: #eee; padding: 1em;\n"
     . "margin: 1em; float: left; font-family: \"courier new\", sans-serif; font-size: 8pt; color: #050; } </style>";
-    drupal_set_html_head($header);
+    drupal_add_html_head($header);
 
     if (isset($warnings_filename)) {
       $warnings = file_get_contents($warnings_filename);