diff --git a/lib/class_final.js b/lib/class_final.js
index 313e1f7..49b4b8a 100644
--- a/lib/class_final.js
+++ b/lib/class_final.js
@@ -24,18 +24,79 @@
 
 var Class = require( __dirname + '/class' );
 
-module.exports = function()
+
+/**
+ * Creates a final class
+ *
+ * @return  {Class}  final class
+ */
+exports = module.exports = function()
+{
+    markFinal( arguments );
+
+    // forward everything to Class
+    var result = Class.apply( this, arguments );
+
+    if ( !Class.isClass( result ) )
+    {
+        finalOverride( result );
+    }
+
+    return result;
+};
+
+
+/**
+ * Creates a final class from a class extend operation
+ *
+ * @return  {Class}  final class
+ */
+exports.extend = function()
+{
+    markFinal( arguments );
+    return Class.extend.apply( this, arguments );
+};
+
+
+/**
+ * Causes a definition to be flagged as final
+ *
+ * This function assumes the last argument to be the definition, which is the
+ * common case, and modifies the object referenced by that argument.
+ *
+ * @param  {arguments}  args  arguments to parse
+ *
+ * @return  {undefined}
+ */
+function markFinal( args )
 {
     // the last argument _should_ be the definition
-    var dfn = arguments[ arguments.length - 1 ];
+    var dfn = args[ args.length - 1 ];
 
     if ( typeof dfn === 'object' )
     {
-        // mark it as final
+        // mark as abstract
         dfn.___$$final$$ = true;
     }
+}
 
-    // forward everything to Class
-    return Class.apply( this, arguments );
-};
+
+/**
+ * Overrides object members to permit final classes
+ *
+ * @param  {Object}  obj  object to override
+ *
+ * @return  {undefined}
+ */
+function finalOverride( obj )
+{
+    var extend = obj.extend;
+
+    // wrap extend, applying the abstract flag
+    obj.extend = function()
+    {
+        markFinal( arguments );
+        return extend.apply( this, arguments );
+    };
+}
 
diff --git a/test/test-class_builder-final.js b/test/test-class_builder-final.js
index 648495e..627e37e 100644
--- a/test/test-class_builder-final.js
+++ b/test/test-class_builder-final.js
@@ -157,3 +157,27 @@ var common  = require( './common' ),
     assert.fail( "Should not be able to extend final classes" );
 } )();
 
+
+/**
+ * Ensure we're able to create final classes by extending existing classes.
+ */
+( function testCanCreateFinalSubtypes()
+{
+    var Foo        = builder.build( {} ),
+        FinalNamed = FinalClass( 'FinalNamed' ).extend( Foo, {} ),
+        FinalAnon  = FinalClass.extend( Foo, {} )
+    ;
+
+    // named
+    assert.throws( function()
+    {
+        FinalNamed.extend( {} );
+    }, Error, "Cannot extend final named subtype" );
+
+    // anonymous
+    assert.throws( function()
+    {
+        FinalAnon.extend( {} );
+    }, Error, "Cannot extend final anonymous subtype" );
+} )();
+