diff --git a/book.php b/book.php
index f18c474..7bf5678 100644
--- a/book.php
+++ b/book.php
@@ -357,6 +357,7 @@ class Book extends Base {
         else
         {
             $data = $this->getDataById ($idData);
+            if (!$data) return NULL;
             $file = $data->name . "." . strtolower ($data->format);
         }
 
diff --git a/fetch.php b/fetch.php
index 1b31b91..f5dafbb 100644
--- a/fetch.php
+++ b/fetch.php
@@ -9,7 +9,14 @@
     require_once ("config.php");
     require_once ("book.php");
     require_once ("data.php");
-     
+
+function notFound () {
+    header($_SERVER["SERVER_PROTOCOL"]." 404 Not Found");
+    header("Status: 404 Not Found");
+
+    $_SERVER['REDIRECT_STATUS'] = 404;
+}
+    
     global $config;
     $expires = 60*60*24*14;
     header("Pragma: public");
@@ -26,6 +33,23 @@
     {
         $book = Book::getBookById($bookId);
     }
+    
+    if (!$book) {
+        notFound ();
+        return;     
+    }
+    
+    if ($book && ($type == "jpg" || empty ($config['calibre_internal_directory']))) {
+        if ($type == "jpg") {
+            $file = $book->getFilePath ($type);
+        } else {
+            $file = $book->getFilePath ($type, $idData);
+        }
+        if (!$file || !file_exists ($file)) {
+            notFound ();
+            return;
+        }
+    }
      
     switch ($type)
     {