diff --git a/sys/dev/serial/sio/sio.c b/sys/dev/serial/sio/sio.c
index 1111111..2222222 100644
--- a/sys/dev/serial/sio/sio.c
+++ b/sys/dev/serial/sio/sio.c
@@ -1475,10 +1475,10 @@ sioclose(struct dev_close_args *ap)
 	if (com->gone) {
 		kprintf("sio%d: gone\n", com->unit);
 		crit_enter();
 		if (com->ibuf != NULL) {
 			kfree(com->ibuf, M_DEVBUF);
+			com->ibuf = NULL;
+			com->iptr = NULL;
 		}
-		bzero(tp, sizeof *tp);
 		crit_exit();
 	}
 	lwkt_reltoken(&tty_token);