diff --git a/lib/arboreal.js b/lib/arboreal.js
index 0135c0c..cca404e 100644
--- a/lib/arboreal.js
+++ b/lib/arboreal.js
@@ -236,8 +236,10 @@
     return nodeList;
   };
 
-  Arboreal.prototype.__defineGetter__("length", function () {
-    return this.toArray().length;
+  Object.defineProperty(Arboreal.prototype, 'length', {
+    get: function() {
+      return this.toArray().length;
+    };
   });