diff --git a/lib/class.js b/lib/class.js
index 716b6d8..557ff5c 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -96,6 +96,17 @@ var extend = ( function( extending )
 
         var properties = {};
         util.propCopy( props, prototype, result_data, {
+            each: function( name, value )
+            {
+                // disallow use of our internal __initProps() method
+                if ( name === '__initProps' )
+                {
+                    throw new Error( "__initProps is a reserved method" );
+                }
+
+                this.performDefault( name, value );
+            },
+
             property: function( name, value )
             {
                 properties[ name ] = value;
diff --git a/test/test-class-extend.js b/test/test-class-extend.js
index 8dccbfa..1e70c8e 100644
--- a/test/test-class-extend.js
+++ b/test/test-class-extend.js
@@ -185,3 +185,11 @@ assert.ok(
     "Subtypes can override parent property values"
 );
 
+assert.throws( function()
+{
+    Class.extend(
+    {
+        __initProps: function() {},
+    });
+}, Error, "__initProps() cannot be declared (internal method)" );
+