diff --git a/lib/weblib.php b/lib/weblib.php
index ce30a8f6923..4cdb1952f2a 100644
--- a/lib/weblib.php
+++ b/lib/weblib.php
@@ -1711,7 +1711,7 @@ function purify_html($text, $options = array()) {
         $config = HTMLPurifier_Config::createDefault();
 
         $config->set('HTML.DefinitionID', 'moodlehtml');
-        $config->set('HTML.DefinitionRev', 2);
+        $config->set('HTML.DefinitionRev', 3);
         $config->set('Cache.SerializerPath', $cachedir);
         $config->set('Cache.SerializerPermissions', $CFG->directorypermissions);
         $config->set('Core.NormalizeNewlines', false);
@@ -1750,6 +1750,9 @@ function purify_html($text, $options = array()) {
             $def->addElement('algebra', 'Inline', 'Inline', array());                   // Algebra syntax, equivalent to @@xx@@.
             $def->addElement('lang', 'Block', 'Flow', array(), array('lang'=>'CDATA')); // Original multilang style - only our hacked lang attribute.
             $def->addAttribute('span', 'xxxlang', 'CDATA');                             // Current very problematic multilang.
+
+            // Use the built-in Ruby module to add annotation support.
+            $def->manager->addModule(new HTMLPurifier_HTMLModule_Ruby());
         }
 
         $purifier = new HTMLPurifier($config);