diff --git a/ponydos.asm b/ponydos.asm
index 953be04..f3388d8 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -38,10 +38,11 @@ start:
 	; Clear BSS
 	;xor al, al
 	mov di, _bss_start
-	mov cx, _bss_end - _bss_start
+	mov cx, _bss_end - _bss_start - 1
 	rep stosb
 
-	mov [boot_disk], dl
+	; At boot_disk
+	mov [di], dl
 
 initialize_mouse:
 	; Initialize mouse
@@ -467,6 +468,7 @@ mouse_buttons resb 1
 mouse_column resb 1
 mouse_row resb 1
 
+; Last thing in bss
 boot_disk resb 1
 
 _bss_end: