diff --git a/mobile.netbiblio.php b/mobile.netbiblio.php
index 3641a21..2067bb9 100644
--- a/mobile.netbiblio.php
+++ b/mobile.netbiblio.php
@@ -249,6 +249,8 @@ class NetBiblio extends WebService
         $files = json_decode($json, true);
         if (is_array($files)) {
             $book['files'] = $files;
+        } else {
+            $book['files'] = array();
         }
         return $book;
     }