diff --git a/hierarchical_select.js b/hierarchical_select.js
index 059fcc8..1e58861 100644
--- a/hierarchical_select.js
+++ b/hierarchical_select.js
@@ -472,7 +472,7 @@ Drupal.HierarchicalSelect.update = function(hsid, updateType, settings) {
     case 'update-hierarchical-select':
       var value = $('#'+ settings.select_id).val();
       var lastUnchanged = parseInt(settings.select_id.replace(/^.*-hierarchical-select-selects-(\d+)$/, "$1")) + 1;
-      var optionClass = $('#'+ settings.select_id).find('option[value='+ value +']').attr('class');
+      var optionClass = $('#'+ settings.select_id).find('option[value="'+ value +'"]').attr('class');
 
       // Don't do anything (also no callback to the server!) when the selected
       // item is: