diff --git a/imagefield_focus.js b/imagefield_focus.js
index 5e0fb23..9b20afc 100644
--- a/imagefield_focus.js
+++ b/imagefield_focus.js
@@ -39,7 +39,7 @@ Drupal.behaviors.imagefield_focus = function(context) {
       var $this = $(this);
       var img = $('> img', $this);
       var inputs = $('input.imagefield-focus', $this.parent());
-      var fieldName = inputs.attr('name').replace(/^([a-z0-9_]+)\[.+$/, '$1');
+      var fieldName = inputs.attr('name').match(/field_[^\[\]]*/, '$1');
       var settings = Drupal.settings.imagefield_focus[fieldName];
 
       var minSize, ratio;