diff --git a/hw/pc.c b/hw/pc.c
index 1c9d89a..4b07b35 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -549,8 +549,7 @@
         /* LGPL'ed VGA BIOS messages */
     case 0x501:
     case 0x502:
-        fprintf(stderr, "VGA BIOS panic, line %d\n", val);
-        exit(1);
+        exit((val << 1) | 1);
     case 0x500:
     case 0x503:
 #ifdef DEBUG_BIOS
@@ -591,6 +590,7 @@
     register_ioport_write(0x403, 1, 1, bochs_bios_write, NULL);
     register_ioport_write(0x8900, 1, 1, bochs_bios_write, NULL);
 
+    register_ioport_write(0x501, 1, 1, bochs_bios_write, NULL);
     register_ioport_write(0x501, 1, 2, bochs_bios_write, NULL);
     register_ioport_write(0x502, 1, 2, bochs_bios_write, NULL);
     register_ioport_write(0x500, 1, 1, bochs_bios_write, NULL);