diff --git a/lib/AudioBook.php b/lib/AudioBook.php
index a099f4e..c624ba8 100644
--- a/lib/AudioBook.php
+++ b/lib/AudioBook.php
@@ -1,6 +1,11 @@
 <?php
 require_once('DbMapping.php');
 
+class BookNotFoundException extends WebException {
+    public function __construct($code) {
+        parent::__construct('BookNotFound', "The book with code $code was not found", -404);
+    }
+}
 
 function convertMSChar($src)
 {
@@ -166,7 +171,7 @@ class AudioBook extends DbMapping
     /**
      * @param $code
      * @return int
-     * @throws Exception
+     * @throws BookNotFoundException
      * @throws SqlException
      */
     public static function findIdByCode($code)
@@ -174,7 +179,7 @@ class AudioBook extends DbMapping
         $sql = "SELECT NoticeId FROM Notices WHERE LTRIM(RTRIM(NoticeNr)) = '$code';";
         $result = Connection::execute($sql, false);
         if ($result === false || $result->length == 0) {
-            throw new Exception("NotFoundException");
+            throw new BookNotFoundException($code);
         }
 
         $row = $result->current();
diff --git a/mobile.netbiblio.php b/mobile.netbiblio.php
index d7f9d24..a921356 100644
--- a/mobile.netbiblio.php
+++ b/mobile.netbiblio.php
@@ -7,12 +7,12 @@
  */
 
 require_once "global.php";
+require_once "mobile.webservice.php";
+
 require_once "lib/AudioBook.php";
 require_once "lib/User.php";
 require_once "lib/BookSearch.php";
 
-require_once "mobile.webservice.php";
-
 class NetBiblio extends WebService
 {
     private $data = array();