diff --git a/hw/ide.c b/hw/ide.c
index d9c02ab0f..0cd252173 100644
--- a/hw/ide.c
+++ b/hw/ide.c
@@ -1729,6 +1729,8 @@ static void ide_ioport_write(void *opaque, uint32_t addr, uint32_t val)
                 goto abort_cmd;
             /* XXX: valid for CDROM ? */
             switch(s->feature) {
+            case 0xcc: /* reverting to power-on defaults enable */
+            case 0x66: /* reverting to power-on defaults disable */
             case 0x02: /* write cache enable */
             case 0x82: /* write cache disable */
             case 0xaa: /* read look-ahead enable */