diff --git a/inc/ZipLib.class.php b/inc/ZipLib.class.php
index 767d324a9b17639911c58d5c067c3dc70dd5d91d..3b39ad1b66e94d06e6023d9b7cd219d9124cb9da 100644
--- a/inc/ZipLib.class.php
+++ b/inc/ZipLib.class.php
@@ -239,7 +239,8 @@ class ZipLib
 
   while ($pos < $size)
   {
-    $byte = @fread($zip, 1); $bytes=($bytes << 8) | Ord($byte);
+    $byte = @fread($zip, 1);
+    $bytes=(($bytes << 8) & 0xFFFFFFFF) | Ord($byte);
     if ($bytes == 0x504b0506){ $pos++; break; } $pos++;
   }