diff --git a/static/js/relearn.js b/static/js/relearn.js
index 85e09d55b7..94c5100ee3 100644
--- a/static/js/relearn.js
+++ b/static/js/relearn.js
@@ -423,7 +423,7 @@ $(function() {
 
 jQuery.extend({
     highlight: function(node, re, nodeName, className) {
-        if (node.nodeType === 3) {
+        if (node.nodeType === 3 && node.parentElement.namespaceURI == 'http://www.w3.org/1999/xhtml') { // text nodes
             var match = node.data.match(re);
             if (match) {
                 var highlight = document.createElement(nodeName || 'span');