diff --git a/grub-core/kern/fs.c b/grub-core/kern/fs.c
index b9508296d..7ad0aaf4e 100644
--- a/grub-core/kern/fs.c
+++ b/grub-core/kern/fs.c
@@ -130,7 +130,7 @@ grub_fs_probe (grub_device_t device)
 struct grub_fs_block
 {
   grub_disk_addr_t offset;
-  unsigned long length;
+  grub_disk_addr_t length;
 };
 
 static grub_err_t