diff --git a/lib/class.js b/lib/class.js
index c692b3b..6ab2544 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -355,13 +355,12 @@ function extend()
     // set up the new class
     var data = class_builder.build.apply( null, arguments ),
 
-        new_class        = data[ 'class' ],
-        abstract_methods = data.abstractMethods,
-        class_id         = data.classId
+        new_class = data[ 'class' ],
+        class_id  = data.classId
     ;
 
     // important: call after setting prototype
-    setupProps( new_class, abstract_methods, class_id );
+    setupProps( new_class, class_id );
 
     // lock down the new class (if supported) to ensure that we can't add
     // members at runtime
@@ -419,46 +418,19 @@ var implement = function()
 /**
  * Sets up common properties for the provided function (class)
  *
- * @param  {function()}      func              function (class) to set up
- * @param  {Array.<string>}  abstract_methods  list of abstract method names
- * @param  {number}          class_id          unique id to assign to class
+ * @param  {function()}  func      function (class) to set up
+ * @param  {number}      class_id  unique id to assign to class
  *
  * @return  {undefined}
  */
-function setupProps( func, abstract_methods, class_id )
+function setupProps( func, class_id )
 {
-    attachAbstract( func, abstract_methods );
     attachExtend( func );
     attachImplement( func );
     attachId( func, class_id );
 }
 
 
-/**
- * Attaches isAbstract() method to the class
- *
- * @param  {Function}  func     function (class) to attach method to
- * @param  {Array}     methods  abstract method names
- *
- * @return  {undefined}
- */
-function attachAbstract( func, methods )
-{
-    var is_abstract = ( methods.__length > 0 ) ? true: false;
-
-    /**
-     * Returns whether the class contains abstract methods (and is therefore
-     * abstract)
-     *
-     * @return  {Boolean}  true if class is abstract, otherwise false
-     */
-    util.defineSecureProp( func, 'isAbstract', function()
-    {
-        return is_abstract;
-    });
-}
-
-
 /**
  * Attaches extend method to the given function (class)
  *
diff --git a/lib/class_builder.js b/lib/class_builder.js
index 3a0d93e..cb1e52a 100644
--- a/lib/class_builder.js
+++ b/lib/class_builder.js
@@ -216,13 +216,14 @@ exports.build = function extend()
     meta.abstractMethods = abstract_methods;
     meta.name            = cname;
 
+    attachAbstract( new_class, abstract_methods );
+
     // we're done with the extension process
     extending = false;
 
     return {
-        'class':         new_class,
-        abstractMethods: abstract_methods,
-        classId:         class_id,
+        'class': new_class,
+        classId: class_id,
     };
 };
 
@@ -726,3 +727,28 @@ exports.isInstanceOf = function( type, instance )
     return false;
 };
 
+
+/**
+ * Attaches isAbstract() method to the class
+ *
+ * @param  {Function}  func     function (class) to attach method to
+ * @param  {Array}     methods  abstract method names
+ *
+ * @return  {undefined}
+ */
+function attachAbstract( func, methods )
+{
+    var is_abstract = ( methods.__length > 0 ) ? true: false;
+
+    /**
+     * Returns whether the class contains abstract methods (and is therefore
+     * abstract)
+     *
+     * @return  {Boolean}  true if class is abstract, otherwise false
+     */
+    util.defineSecureProp( func, 'isAbstract', function()
+    {
+        return is_abstract;
+    });
+}
+