diff --git a/src/disk/hdc_esdi_mca.c b/src/disk/hdc_esdi_mca.c
index 78a2f3183..b3c33675a 100644
--- a/src/disk/hdc_esdi_mca.c
+++ b/src/disk/hdc_esdi_mca.c
@@ -1220,6 +1220,12 @@ esdi_mca_write(int port, uint8_t val, void *priv)
 
     if (!(dev->pos_regs[3] & 8)) {
         switch (dev->pos_regs[3] & 7) {
+            case 0:
+                dev->bios = 0xc0000;
+                break;
+            case 1:
+                dev->bios = 0xc4000;
+                break;
             case 2:
                 dev->bios = 0xc8000;
                 break;