diff --git a/lib/formslib.php b/lib/formslib.php
index b6f0c179a16..88564a784ad 100644
--- a/lib/formslib.php
+++ b/lib/formslib.php
@@ -2905,7 +2905,7 @@ class MoodleQuickForm_Rule_Required extends HTML_QuickForm_Rule {
         global $CFG;
         if (!empty($CFG->strictformsrequired)) {
             if (!empty($format) && $format == FORMAT_HTML) {
-                return array('', "{jsVar}.replace(/(<[^img|hr|canvas]+>)|&nbsp;|\s+/ig, '') == ''");
+                return array('', "{jsVar}.replace(/(<(?!img|hr|canvas)[^>]*>)|&nbsp;|\s+/ig, '') == ''");
             } else {
                 return array('', "{jsVar}.replace(/^\s+$/g, '') == ''");
             }