diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
index 9e60d2a0edc1..7397495de4d6 100644
--- a/drivers/staging/comedi/drivers/comedi_test.c
+++ b/drivers/staging/comedi/drivers/comedi_test.c
@@ -790,7 +790,7 @@ static void waveform_detach(struct comedi_device *dev)
 {
 	struct waveform_private *devpriv = dev->private;
 
-	if (devpriv) {
+	if (devpriv && dev->n_subdevices) {
 		del_timer_sync(&devpriv->ai_timer);
 		del_timer_sync(&devpriv->ao_timer);
 	}