diff --git a/jquery.popupwindow.js b/jquery.popupwindow.js
index 9a00de7..e5aaa2f 100644
--- a/jquery.popupwindow.js
+++ b/jquery.popupwindow.js
@@ -21,7 +21,7 @@
     width:       500
   };
 
-  $.popupWindow = function(url, opts) {
+  $.fn.popupWindow = function(url, opts) {
     var options = $.extend({}, defaults, opts);
 
     // center the window