diff --git a/drivers/staging/comedi/drivers/comedi_fc.h b/drivers/staging/comedi/drivers/comedi_fc.h
index 042bf87918c649b46686af8c1bdb50a792a7645b..b8d125e81a0f03d5e0ef6caa4818f596aca92eba 100644
--- a/drivers/staging/comedi/drivers/comedi_fc.h
+++ b/drivers/staging/comedi/drivers/comedi_fc.h
@@ -47,19 +47,20 @@ unsigned int cfc_handle_events(struct comedi_device *,
 
 static inline unsigned int cfc_bytes_per_scan(struct comedi_subdevice *s)
 {
-	int num_samples;
-	int bits_per_sample;
+	unsigned int chanlist_len = s->async->cmd.chanlist_len;
+	unsigned int num_samples;
+	unsigned int bits_per_sample;
 
 	switch (s->type) {
 	case COMEDI_SUBD_DI:
 	case COMEDI_SUBD_DO:
 	case COMEDI_SUBD_DIO:
 		bits_per_sample = 8 * bytes_per_sample(s);
-		num_samples = (s->async->cmd.chanlist_len +
-			       bits_per_sample - 1) / bits_per_sample;
+		num_samples = (chanlist_len + bits_per_sample - 1) /
+				bits_per_sample;
 		break;
 	default:
-		num_samples = s->async->cmd.chanlist_len;
+		num_samples = chanlist_len;
 		break;
 	}
 	return num_samples * bytes_per_sample(s);