diff -ur syslinux-3.51.orig/cpuinit.inc syslinux-3.51/cpuinit.inc
--- syslinux-3.51.orig/cpuinit.inc	2007-06-10 18:51:39.000000000 -0400
+++ syslinux-3.51/cpuinit.inc	2007-06-17 11:37:19.000000000 -0400
@@ -48,12 +48,10 @@
 		rep movsd
 
 ;
-; Check if we're 386 (as opposed to 486+); if so we need to blank out
-; the WBINVD instruction
+; Determine if we're running on a 64-bit CPU
 ;
-; We check for 486 by setting EFLAGS.AC
+; First, check if we're 386. If so, we need to blank out the WBINVD instruction
 ;
-%if DO_WBINVD
 		pushfd				; Save the good flags
 		pushfd
 		pop eax
@@ -69,6 +67,37 @@
 ;
 ; 386 - Looks like we better blot out the WBINVD instruction
 ;
+%if DO_WBINVD
 		mov byte [try_wbinvd],0c3h		; Near RET
-is_486:
 %endif	; DO_WBINVD
+		jmp is_32bit
+is_486:
+;
+; Check if this CPU supports the CPUID command
+;
+		pushfd				; Save the flags again
+		pushfd
+		pop eax
+		mov ebx,eax
+		xor eax,(1 << 21)		; CPUID bit
+		push eax
+		popfd
+		pushfd
+		pop eax
+		popfd				; Restore the original flags
+		xor eax,ebx
+		jz is_32bit
+;
+; Now check for the 64-bit flag in bit 29 of the Extended CPU features byte,
+; ($8000_0001, edx).
+;
+		mov eax, 80000000h		; Find last extended CPUID #
+		cpuid
+		cmp eax, 80000000h
+		jbe is_32bit
+		mov eax, 80000001h		; Read Extended CPU flags
+		cpuid
+		bt edx, 29			; 64-bit if bit 29 is set
+		jnc is_32bit
+		mov byte [Is64Bit],1		; Flag that we're 64-bit
+is_32bit:
diff -ur syslinux-3.51.orig/keywords syslinux-3.51/keywords
--- syslinux-3.51.orig/keywords	2007-06-10 18:51:39.000000000 -0400
+++ syslinux-3.51/keywords	2007-06-17 11:37:19.000000000 -0400
@@ -4,6 +4,7 @@
 append
 config
 default
+default64
 display
 font
 implicit
diff -ur syslinux-3.51.orig/keywords.inc syslinux-3.51/keywords.inc
--- syslinux-3.51.orig/keywords.inc	2007-06-10 18:51:39.000000000 -0400
+++ syslinux-3.51/keywords.inc	2007-06-17 11:37:19.000000000 -0400
@@ -50,6 +50,7 @@
 		keyword include,	pc_filecmd,	pc_include
 		keyword append,		pc_append
 		keyword default,	pc_default
+		keyword default64,	pc_default64
 		keyword display,	pc_filecmd,	get_msg_file
 		keyword font,		pc_filecmd,	loadfont
 		keyword implicit,	pc_setint16,	AllowImplicit
diff -ur syslinux-3.51.orig/kwdhash.gen syslinux-3.51/kwdhash.gen
--- syslinux-3.51.orig/kwdhash.gen	2007-06-10 18:51:45.000000000 -0400
+++ syslinux-3.51/kwdhash.gen	2007-06-17 11:37:19.000000000 -0400
@@ -4,6 +4,7 @@
 hash_append             equ 0xc53999a4
 hash_config             equ 0xc0c69547
 hash_default            equ 0xcc5159ed
+hash_default64          equ 0x4567b1c5
 hash_display            equ 0xd509bc40
 hash_font               equ 0x0032b1b4
 hash_implicit           equ 0xa6f50207
diff -ur syslinux-3.51.orig/layout.inc syslinux-3.51/layout.inc
--- syslinux-3.51.orig/layout.inc	2007-06-10 18:51:39.000000000 -0400
+++ syslinux-3.51/layout.inc	2007-06-17 11:38:08.000000000 -0400
@@ -26,7 +26,7 @@
 ; The secondary BSS section, above the text; we really wish we could
 ; just make it follow .bcopy32 or hang off the end,
 ; but it doesn't seem to work that way.
-LATEBSS_START	equ 0B300h
+LATEBSS_START	equ 0B310h
 
 ; Reserve memory for the stack.  This causes checkov to abort the
 ; compile if we violate this space.
diff -ur syslinux-3.51.orig/parseconfig.inc syslinux-3.51/parseconfig.inc
--- syslinux-3.51.orig/parseconfig.inc	2007-06-10 18:51:39.000000000 -0400
+++ syslinux-3.51/parseconfig.inc	2007-06-17 11:37:19.000000000 -0400
@@ -20,7 +20,20 @@
 ;
 ; "default" command
 ;
-pc_default:	mov di,default_cmd
+pc_default:	cmp byte [HasDefault64],0	; Check if we accepted 'default64'
+		ja pc_getline			; If so, do nothing
+		mov di,default_cmd
+		call getline
+		mov byte [di-1],0		; null-terminate
+		ret
+
+;
+; "default64" command
+;
+pc_default64:	cmp byte [Is64Bit],0		; Make sure cpu is 64-bit
+		je pc_getline
+		mov byte [HasDefault64],1	; Note that we saw a default64
+		mov di,default_cmd
 		call getline
 		mov byte [di-1],0		; null-terminate
 		ret
@@ -431,6 +444,8 @@
 SerialPort	dw 0			; Serial port base (or 0 for no serial port)
 VKernelBytes	dw 0			; Number of bytes used by vkernels
 VKernel		db 0			; Have we seen any "label" statements?
+Is64Bit		db 0			; Is this CPU 64-bit?
+HasDefault64	db 0			; We've seen a 'default64' statement
 
 %if IS_PXELINUX
 IPAppend	db 0			; Default IPAPPEND option