diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index fdda9ec625ad..dde392b91bb3 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -718,6 +718,12 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
 	if (guest_cid > U32_MAX)
 		return -EINVAL;
 
+	/* Refuse if CID is assigned to the guest->host transport (i.e. nested
+	 * VM), to make the loopback work.
+	 */
+	if (vsock_find_cid(guest_cid))
+		return -EADDRINUSE;
+
 	/* Refuse if CID is already in use */
 	mutex_lock(&vhost_vsock_mutex);
 	other = vhost_vsock_get(guest_cid);