diff --git a/sys/pc98/cbus/sio.c b/sys/pc98/cbus/sio.c
index 636d75356f4..210e21ef9fe 100644
--- a/sys/pc98/cbus/sio.c
+++ b/sys/pc98/cbus/sio.c
@@ -785,7 +785,8 @@ siodetach(dev)
 		return (0);
 	}
 	com->gone = TRUE;
-	ttygone(com->tp);
+	if (com->tp)
+		ttygone(com->tp);
 	for (i = 0 ; i < 6; i++)
 		destroy_dev(com->devs[i]);
 	if (com->irqres) {
diff --git a/sys/pc98/pc98/sio.c b/sys/pc98/pc98/sio.c
index 636d75356f4..210e21ef9fe 100644
--- a/sys/pc98/pc98/sio.c
+++ b/sys/pc98/pc98/sio.c
@@ -785,7 +785,8 @@ siodetach(dev)
 		return (0);
 	}
 	com->gone = TRUE;
-	ttygone(com->tp);
+	if (com->tp)
+		ttygone(com->tp);
 	for (i = 0 ; i < 6; i++)
 		destroy_dev(com->devs[i]);
 	if (com->irqres) {