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..aff7e46 100644
--- a/Behavioral/Iterator/BookListIterator.php
+++ b/Behavioral/Iterator/BookListIterator.php
@@ -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..5ab2be9 100644
--- a/Behavioral/Iterator/BookListReverseIterator.php
+++ b/Behavioral/Iterator/BookListReverseIterator.php
@@ -11,13 +11,14 @@ class BookListReverseIterator extends BookListIterator
         $this->currentBook = $this->bookList->count() - 1;
     }
 
+    /**
+     * (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--;
     }
-
-    public function valid()
-    {
-        return 0 <= $this->currentBook;
-    }
 }