diff --git a/blockdev.h b/blockdev.h
index 1c9ca6a..d73d552 100644
--- a/blockdev.h
+++ b/blockdev.h
@@ -19,7 +19,11 @@ void blockdev_auto_del(BlockDriverState *bs);
 
 typedef enum {
     IF_DEFAULT = -1,            /* for use with drive_add() only */
-    IF_IDE,                     /* machines without block_default_type get 0 */
+    /*
+     * IF_IDE must be zero, because we want QEMUMachine member
+     * block_default_type to default-initialize to IF_IDE
+     */
+    IF_IDE = 0,
     IF_NONE,
     IF_SCSI, IF_FLOPPY, IF_PFLASH, IF_MTD, IF_SD, IF_VIRTIO, IF_XEN,
     IF_COUNT