diff --git a/include/fat.h b/include/fat.h
index 4c92442..f1b4a0d 100644
--- a/include/fat.h
+++ b/include/fat.h
@@ -178,12 +178,12 @@ typedef struct dir_slot {
 typedef struct {
 	__u8	*fatbuf;	/* Current FAT buffer */
 	int	fatsize;	/* Size of FAT in bits */
-	__u16	fatlength;	/* Length of FAT in sectors */
+	__u32	fatlength;	/* Length of FAT in sectors */
 	__u16	fat_sect;	/* Starting sector of the FAT */
-	__u16	rootdir_sect;	/* Start sector of root directory */
+	__u32	rootdir_sect;	/* Start sector of root directory */
 	__u16	sect_size;	/* Size of sectors in bytes */
 	__u16	clust_size;	/* Size of clusters in sectors */
-	short	data_begin;	/* The sector of the first cluster, can be negative */
+	int	data_begin;	/* The sector of the first cluster, can be negative */
 	int	fatbufnum;	/* Used by get_fatent, init to -1 */
 } fsdata;