Index: sys/boot/i386/pmbr/pmbr.s
===================================================================
--- sys/boot/i386/pmbr/pmbr.s	(revision 224700)
+++ sys/boot/i386/pmbr/pmbr.s	(working copy)
@@ -36,6 +36,7 @@
 
 		.set LOAD,0x7c00		# Load address
 		.set EXEC,0x600 		# Execution address
+		.set ARG,0x900			# Arguments
 		.set MAGIC,0xaa55		# Magic: bootable
 		.set SECSIZE,0x200		# Size of a single disk sector
 		.set DISKSIG,440		# Disk signature offset
@@ -93,7 +94,8 @@ main.1: 	movb $0x80,%dl			# Assume drive 0x80
 #
 # Load the primary GPT header from LBA 1 and verify signature.
 #
-main.2:		movw $GPT_ADDR,%bx
+main.2:		mov %dx,ARG			# Save drive number
+		movw $GPT_ADDR,%bx
 		movw $lba,%si
 		call read
 		cmpl $GPT_SIG_0,GPT_ADDR+GPT_SIG