Index: /trunk/src/VBox/Devices/PC/BIOS/rombios.c
===================================================================
--- /trunk/src/VBox/Devices/PC/BIOS/rombios.c	(revision 37034)
+++ /trunk/src/VBox/Devices/PC/BIOS/rombios.c	(revision 37035)
@@ -2631,5 +2631,5 @@
           for (i = 0; i < 0xf; i++)
               sum += read_byte(ebda_seg, fdpt + i);
-          sum = 1 - sum;
+          sum = -sum;
           write_byte(ebda_seg, fdpt + 0x0f, sum);
       }