diff --git a/AltairZ80/wd179x.c b/AltairZ80/wd179x.c
index dc8be1f6..82563b28 100644
--- a/AltairZ80/wd179x.c
+++ b/AltairZ80/wd179x.c
@@ -107,6 +107,7 @@ typedef struct {
     uint8 fdc_head;     /* H Head Number */
     uint8 sel_drive;    /* Currently selected drive */
     uint8 drivetype;    /* 8 or 5 depending on disk type. */
+    /* Note: the fields above must be kept in sync with WD179X_INFO_PUB */
     uint8 fdc_status;   /* WD179X Status Register */
     uint8 verify;       /* WD179X Type 1 command Verify flag */
     uint8 fdc_data;     /* WD179X Data Register */
diff --git a/AltairZ80/wd179x.h b/AltairZ80/wd179x.h
index 18971b65..17f88e0d 100644
--- a/AltairZ80/wd179x.h
+++ b/AltairZ80/wd179x.h
@@ -51,8 +51,10 @@ extern uint8 wd179x_get_nheads(void);
 #define WD179X_SECTOR 2
 #define WD179X_DATA   3
 
+/* Note: this struct must be kept in sync with WD179X_INFO */
 typedef struct {
     PNP_INFO pnp;       /* Plug-n-Play Information */
+    uint16 fdctype;     /* Default is 1793 */
     uint8 intrq;        /* WD179X Interrupt Request Output (EOJ) */
     uint8 hld;          /* WD179X Head Load Output */
     uint8 drq;          /* WD179X DMA Request Output */