diff --git a/drivers/rptun/rptun.c b/drivers/rptun/rptun.c
index 3a0bf76dc7e..61fc4782ad3 100644
--- a/drivers/rptun/rptun.c
+++ b/drivers/rptun/rptun.c
@@ -1262,15 +1262,15 @@ int rptun_panic(FAR const char *cpuname)
 int rptun_buffer_nused(FAR struct rpmsg_virtio_device *rvdev, bool rx)
 {
   FAR struct virtqueue *vq = rx ? rvdev->rvq : rvdev->svq;
+  uint16_t nused = vq->vq_ring.avail->idx - vq->vq_ring.used->idx;
 
   if ((rpmsg_virtio_get_role(rvdev) == RPMSG_MASTER) ^ rx)
     {
-      return vq->vq_ring.avail->idx - vq->vq_ring.used->idx;
+      return nused;
     }
   else
     {
-      return vq->vq_nentries -
-             (vq->vq_ring.avail->idx - vq->vq_ring.used->idx);
+      return vq->vq_nentries - nused;
     }
 }