diff --git a/src/usr.sbin/ntpd/client.c b/src/usr.sbin/ntpd/client.c
index 70560973..f877e1f9 100644
--- a/src/usr.sbin/ntpd/client.c
+++ b/src/usr.sbin/ntpd/client.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: client.c,v 1.10 2004/07/06 19:06:43 henning Exp $ */
+/*	$OpenBSD: client.c,v 1.11 2004/07/06 23:26:38 henning Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -138,16 +138,19 @@ client_dispatch(struct ntp_peer *p)
 	T2 = lfp_to_d(msg.rectime);
 	T3 = lfp_to_d(msg.xmttime);
 
-	p->offset[p->shift] = ((T2 - T1) + (T3 - T4)) / 2;
-	p->delay[p->shift] = (T2 - T1) - (T3 - T4);
+	p->reply[p->shift].offset = ((T2 - T1) + (T3 - T4)) / 2;
+	p->reply[p->shift].delay = (T4 - T1) - (T2 - T3);
+	p->reply[p->shift].error = (T2 - T1) - (T3 - T4);
+	p->reply[p->shift].rcvd = time(NULL);
+	p->reply[p->shift].good = 1;
 
 	p->state = STATE_REPLY_RECEIVED;
 	p->next = time(NULL) + INTERVAL_QUERY;
 	p->deadline = 0;
 
 	log_debug("reply received from %s: offset %f delay %f",
-	    log_sockaddr((struct sockaddr *)&fsa), p->offset[p->shift],
-	    p->delay[p->shift]);
+	    log_sockaddr((struct sockaddr *)&fsa), p->reply[p->shift].offset,
+	    p->reply[p->shift].delay);
 
 	if (++p->shift >= OFFSET_ARRAY_SIZE) {
 		p->shift = 0;
diff --git a/src/usr.sbin/ntpd/ntp.c b/src/usr.sbin/ntpd/ntp.c
index 9f4a980a..05788e33 100644
--- a/src/usr.sbin/ntpd/ntp.c
+++ b/src/usr.sbin/ntpd/ntp.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntp.c,v 1.11 2004/07/05 22:12:53 henning Exp $ */
+/*	$OpenBSD: ntp.c,v 1.12 2004/07/06 23:26:38 henning Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -39,6 +39,7 @@ void	ntp_sighdlr(int);
 int	ntp_dispatch_imsg(void);
 int	ntp_dispatch(int fd);
 void	ntp_adjtime(struct ntpd_conf *);
+int	get_peer_update(struct ntp_peer *, double *);
 
 void
 ntp_sighdlr(int sig)
@@ -283,16 +284,15 @@ void
 ntp_adjtime(struct ntpd_conf *conf)
 {
 	struct ntp_peer	*p;
-	double		 offset_median = 0;
+	double		 offset, offset_median = 0;
 	int		 offset_cnt = 0;
-	u_int8_t	 idx;
 
 	TAILQ_FOREACH(p, &conf->ntp_peers, entry) {
 		if (!p->valid)
 			continue;
 
-		for (idx = 0; idx < OFFSET_ARRAY_SIZE; idx++) {
-			offset_median += p->offset[idx];
+		if (get_peer_update(p, &offset) == 0) {
+			offset_median += offset;
 			offset_cnt++;
 		}
 	}
@@ -303,3 +303,41 @@ ntp_adjtime(struct ntpd_conf *conf)
 		imsg_compose(&ibuf_main, IMSG_ADJTIME, 0,
 			    &offset_median, sizeof(offset_median));
 }
+
+int
+get_peer_update(struct ntp_peer *p, double *offset)
+{
+	int	i, best = 0, good = 0;
+
+	/*
+	 * clock filter
+	 * find the offset which arrived with the lowest delay
+	 * use that as the peer update
+	 * invalidate it and all older ones
+	 */
+
+	for (i = 0; good == 0 && i < OFFSET_ARRAY_SIZE; i++)
+		if (p->reply[i].good) {
+			good++;
+			best = i;
+		}
+
+	for (; i < OFFSET_ARRAY_SIZE; i++)
+		if (p->reply[i].good) {
+			good++;
+			if (p->reply[i].delay < p->reply[best].delay)
+				best = i;
+		}
+
+	/* XXX lower trust in the peer when too few good replies received */
+
+	if (good == 0)
+		return (-1);
+
+	for (i = 0; i < OFFSET_ARRAY_SIZE; i++)
+		if (p->reply[i].rcvd <= p->reply[best].rcvd)
+			p->reply[i].good = 0;
+
+	*offset = p->reply[best].offset;
+	return (0);
+}
diff --git a/src/usr.sbin/ntpd/ntpd.h b/src/usr.sbin/ntpd/ntpd.h
index ea083392..795fd55f 100644
--- a/src/usr.sbin/ntpd/ntpd.h
+++ b/src/usr.sbin/ntpd/ntpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntpd.h,v 1.12 2004/07/05 22:12:53 henning Exp $ */
+/*	$OpenBSD: ntpd.h,v 1.13 2004/07/06 23:26:38 henning Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -36,7 +36,7 @@
 #define	NTPD_OPT_VERBOSE	0x0001
 #define	NTPD_OPT_VERBOSE2	0x0002
 
-#define	INTERVAL_ADJTIME	120	/* call adjtime every n seconds */
+#define	INTERVAL_ADJTIME	240	/* call adjtime every n seconds */
 #define	INTERVAL_QUERY		30	/* sync with peers every n seconds */
 #define	QUERYTIME_MAX		15	/* single query might take n secs max */
 #define	OFFSET_ARRAY_SIZE	8
@@ -53,6 +53,14 @@ struct listen_addr {
 	int				 fd;
 };
 
+struct ntp_offset {
+	u_int8_t	good;
+	double		offset;
+	double		delay;
+	double		error;
+	time_t		rcvd;
+};
+
 struct ntp_peer {
 	TAILQ_ENTRY(ntp_peer)		 entry;
 	struct sockaddr_storage		 ss;
@@ -60,8 +68,7 @@ struct ntp_peer {
 	enum client_state		 state;
 	time_t				 next;
 	time_t				 deadline;
-	double				 offset[OFFSET_ARRAY_SIZE];
-	double				 delay[OFFSET_ARRAY_SIZE];
+	struct ntp_offset		 reply[OFFSET_ARRAY_SIZE];
 	u_int8_t			 shift;
 	u_int8_t			 valid;
 };