diff -uNr a/hw/xen_platform.c b/hw/xen_platform.c
--- a/hw/xen_platform.c	2008-07-24 10:55:59.960084000 +0100
+++ b/hw/xen_platform.c	2008-07-24 11:19:50.310084450 +0100
@@ -59,7 +59,10 @@
     case 0: /* Platform flags */ {
         hvmmem_type_t mem_type = (val & PFFLAG_ROM_LOCK) ?
             HVMMEM_ram_ro : HVMMEM_ram_rw;
-        if (xc_hvm_set_mem_type(xc_handle, domid, mem_type, 0xc0, 0x40))
+        /* The numbers passed below are pfns and page counts representing the memory ranges:
+           0xc0000 - 0xdffff - VGABIOS and option ROMS (extboot, ethboot, etc)
+           0xf0000 - 0xfffff - the main ROMBIOS */
+        if (xc_hvm_set_mem_type(xc_handle, domid, mem_type, 0xc0, 0x20) || xc_hvm_set_mem_type(xc_handle, domid, mem_type, 0xf0, 0x10))
             fprintf(logfile,"xen_platform: unable to change ro/rw "
                     "state of ROM memory area!\n");
         else