diff --git a/boot/fat.asm b/boot/fat.asm
index 5a71de7..d06e5dd 100644
--- a/boot/fat.asm
+++ b/boot/fat.asm
@@ -75,7 +75,7 @@ read:		push ax
 		; dl bit 6-7: cylinder bits 8-9
 		mov cx, dx
 		mov dh, al
-		mov dl, [bp+bpb.drivenum]
+		mov dl, [bp-1]
 		mov ax, 0x0201
 		mov bx, di
 
@@ -128,7 +128,7 @@ resetbuf:	; DS = ES
 		ret
 
 main:		mov bp, params
-		mov [bp+bpb.drivenum], dl
+		mov [bp-1], dl
 
 		; load root directory
 		call resetbuf
diff --git a/inc/bpb.asm b/inc/bpb.asm
index cefec16..f2e170a 100644
--- a/inc/bpb.asm
+++ b/inc/bpb.asm
@@ -11,8 +11,4 @@ struc bpb
 .heads:		resw 1 ; WORD number of sides
 .sectoroffset:	resd 1 ; DWORD partition offset
 .longtotal:	resd 1 ; DWORD large total sectors
-.drivenum:	resb 1 ; BYTE drive number
-.flags:		resb 1
-.signature:	resb 1 ; BYTE 28h
-.serial:	resb 4 ; DWORD serial
 endstruc