Index: tools/mkfat.py
===================================================================
--- tools/mkfat.py	(revision de4a1cf760bebd7fbbda6a9557a99cde8b9aa171)
+++ tools/mkfat.py	(revision 6284978581040c06c173f1990897a36fe2cd2cb2)
@@ -404,5 +404,5 @@
 	boot_sector.drive = 0x80
 	boot_sector.extboot_signature = 0x29
-	boot_sector.serial = random.randint(0, 0xFFFFFFFF)
+	boot_sector.serial = random.randint(0, 0x7fffffff)
 	boot_sector.label = "HELENOS"
 	boot_sector.fstype = "FAT16   "