diff --git a/Behavioral/Iterator/BookList.php b/Behavioral/Iterator/BookList.php
index 6fcf265..9c0b9d4 100644
--- a/Behavioral/Iterator/BookList.php
+++ b/Behavioral/Iterator/BookList.php
@@ -9,7 +9,7 @@ class BookList implements \Countable
 
     public function getBook($bookNumberToGet)
     {
-        if ((int)$bookNumberToGet <= $this->count()) {
+        if (isset($this->books[$bookNumberToGet])) {
             return $this->books[$bookNumberToGet];
         }
 
diff --git a/Behavioral/Iterator/BookListIterator.php b/Behavioral/Iterator/BookListIterator.php
index bc15ffb..93df6d7 100644
--- a/Behavioral/Iterator/BookListIterator.php
+++ b/Behavioral/Iterator/BookListIterator.php
@@ -8,7 +8,7 @@ class BookListIterator implements \Iterator
     /**
      * @var BookList
      */
-    protected $bookList;
+    private $bookList;
 
     /**
      * @var int
@@ -61,7 +61,7 @@ class BookListIterator implements \Iterator
      */
     public function valid()
     {
-        return $this->currentBook < $this->bookList->count();
+        return null !== $this->bookList->getBook($this->currentBook);
     }
 
     /**
diff --git a/Behavioral/Iterator/BookListReverseIterator.php b/Behavioral/Iterator/BookListReverseIterator.php
index 973bd0b..d7ec49a 100644
--- a/Behavioral/Iterator/BookListReverseIterator.php
+++ b/Behavioral/Iterator/BookListReverseIterator.php
@@ -2,22 +2,77 @@
 
 namespace DesignPatterns\Behavioral\Iterator;
 
-class BookListReverseIterator extends BookListIterator
+class BookListReverseIterator implements \Iterator
 {
 
+    /**
+     * @var BookList
+     */
+    private $bookList;
+
+    /**
+     * @var int
+     */
+    protected $currentBook = 0;
+
     public function __construct(BookList $bookList)
     {
         $this->bookList = $bookList;
         $this->currentBook = $this->bookList->count() - 1;
     }
 
+    /**
+     * Return the current book
+     * @link http://php.net/manual/en/iterator.current.php
+     * @return Book Can return any type.
+     */
+    public function current()
+    {
+        return $this->bookList->getBook($this->currentBook);
+    }
+
+    /**
+     * (PHP 5 &gt;= 5.0.0)<br/>
+     * Move forward to next element
+     * @link http://php.net/manual/en/iterator.next.php
+     * @return void Any returned value is ignored.
+     */
     public function next()
     {
         $this->currentBook--;
     }
 
+    /**
+     * (PHP 5 &gt;= 5.0.0)<br/>
+     * Return the key of the current element
+     * @link http://php.net/manual/en/iterator.key.php
+     * @return mixed scalar on success, or null on failure.
+     */
+    public function key()
+    {
+        return $this->currentBook;
+    }
+
+    /**
+     * (PHP 5 &gt;= 5.0.0)<br/>
+     * Checks if current position is valid
+     * @link http://php.net/manual/en/iterator.valid.php
+     * @return boolean The return value will be casted to boolean and then evaluated.
+     *       Returns true on success or false on failure.
+     */
     public function valid()
     {
-        return 0 <= $this->currentBook;
+        return null !== $this->bookList->getBook($this->currentBook);
+    }
+
+    /**
+     * (PHP 5 &gt;= 5.0.0)<br/>
+     * Rewind the Iterator to the first element
+     * @link http://php.net/manual/en/iterator.rewind.php
+     * @return void Any returned value is ignored.
+     */
+    public function rewind()
+    {
+        $this->currentBook = $this->bookList->count() - 1;
     }
 }