Index: ioemu/block.c
===================================================================
--- ioemu.orig/block.c	2007-05-03 14:55:04.000000000 +0100
+++ ioemu/block.c	2007-05-03 14:59:20.000000000 +0100
@@ -420,6 +420,8 @@
 
     if (!bs->inserted)
         return -1;
+    if (sector_num < 0)
+	return -1;
 
     while (nb_sectors > 0) {
         if (sector_num == 0 && bs->boot_sector_enabled) {
@@ -458,6 +460,8 @@
         return -1;
     if (bs->read_only)
         return -1;
+    if (sector_num < 0)
+	return -1;
     if (sector_num == 0 && bs->boot_sector_enabled && nb_sectors > 0) {
         memcpy(bs->boot_sector_data, buf, 512);   
     }