diff --git a/lib/outputcomponents.php b/lib/outputcomponents.php
index 5157293..ae6a17d 100644
--- a/lib/outputcomponents.php
+++ b/lib/outputcomponents.php
@@ -1014,6 +1014,20 @@ class html_writer {
      * @return string HTML fragment
      */
     public static function tag($tagname, $contents, array $attributes = null) {
+        global $PAGE;
+        if ($PAGE->theme->doctype == 'xhtml' || $PAGE->theme->doctype == 'xhtml5' || $PAGE->theme->doctype == 'html5'){
+            // Void tags copied directly from HTML5 specification.
+            // http://www.w3.org/TR/html5/syntax.html#elements-0
+            $voidtags = 'area,base,br,col,embed,hr,img,input,keygen,link,meta,param,source,track,wbr';
+            $voidtags = explode(',', $voidtags);
+            if (in_array(strtolower($tagname), $voidtags)) {
+                if (!empty($contents)) {
+                    throw new coding_exception('Void tag '.$tagname.' cannot have contents');
+                } else {
+                    return self::empty_tag($tagname, $attributes);
+                }
+            }
+        }
         return self::start_tag($tagname, $attributes) . $contents . self::end_tag($tagname);
     }