diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index 80e140e..e7f5ef9 100644
--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -260,13 +260,13 @@
  * newReno in increase case.
  * We work it out by following the idea from TCP-LP's paper directly
  */
-static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, ktime_t last)
+static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, s32 rtt_us)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct lp *lp = inet_csk_ca(sk);
 
-	if (!ktime_equal(last, net_invalid_timestamp()))
-		tcp_lp_rtt_sample(sk,  ktime_to_us(net_timedelta(last)));
+	if (rtt_us > 0)
+		tcp_lp_rtt_sample(sk, rtt_us);
 
 	/* calc inference */
 	if (tcp_time_stamp > tp->rx_opt.rcv_tsecr)