diff --git a/Prototype/Prototype.php b/Prototype/Prototype.php
index 00036b2..ba94e13 100644
--- a/Prototype/Prototype.php
+++ b/Prototype/Prototype.php
@@ -21,7 +21,7 @@ abstract class BookPrototype
      * @abstract
      * @return void
      */
-    abstract function __clone();
+    abstract public function __clone();
 
     public function getTitle()
     {
@@ -62,4 +62,4 @@ $barPrototype = new BarBookPrototype();
 for ($i = 0; $i < 10000; $i++) {
     $book = clone $fooPrototype;
     $book->setTitle('Foo Book No ' . $i);
-}
\ No newline at end of file
+}