diff --git a/vendor/github.com/hashicorp/serf/coordinate/client.go b/vendor/github.com/hashicorp/serf/coordinate/client.go
index 403ec7801..3582ee4da 100644
--- a/vendor/github.com/hashicorp/serf/coordinate/client.go
+++ b/vendor/github.com/hashicorp/serf/coordinate/client.go
@@ -6,6 +6,8 @@ import (
 	"sort"
 	"sync"
 	"time"
+
+	"github.com/armon/go-metrics"
 )
 
 // Client manages the estimated network coordinate for a given node, and adjusts
@@ -205,10 +207,19 @@ func (c *Client) Update(node string, other *Coordinate, rtt time.Duration) (*Coo
 		return nil, err
 	}
 
+	// The code down below can handle zero RTTs, which we have seen in
+	// https://github.com/hashicorp/consul/issues/3789, presumably in
+	// environments with coarse-grained monotonic clocks (we are still
+	// trying to pin this down). In any event, this is ok from a code PoV
+	// so we don't need to alert operators with spammy messages. We did
+	// add a counter so this is still observable, though.
 	const maxRTT = 10 * time.Second
-	if rtt <= 0 || rtt > maxRTT {
+	if rtt < 0 || rtt > maxRTT {
 		return nil, fmt.Errorf("round trip time not in valid range, duration %v is not a positive value less than %v ", rtt, maxRTT)
 	}
+	if rtt == 0 {
+		metrics.IncrCounter([]string{"serf", "coordinate", "zero-rtt"}, 1)
+	}
 
 	rttSeconds := c.latencyFilter(node, rtt.Seconds())
 	c.updateVivaldi(other, rttSeconds)
diff --git a/vendor/github.com/hashicorp/serf/serf/ping_delegate.go b/vendor/github.com/hashicorp/serf/serf/ping_delegate.go
index a4c44028e..98032c5be 100644
--- a/vendor/github.com/hashicorp/serf/serf/ping_delegate.go
+++ b/vendor/github.com/hashicorp/serf/serf/ping_delegate.go
@@ -68,7 +68,8 @@ func (p *pingDelegate) NotifyPingComplete(other *memberlist.Node, rtt time.Durat
 	before := p.serf.coordClient.GetCoordinate()
 	after, err := p.serf.coordClient.Update(other.Name, &coord, rtt)
 	if err != nil {
-		p.serf.logger.Printf("[ERR] serf: Rejected coordinate from %s: %v\n",
+		metrics.IncrCounter([]string{"serf", "coordinate", "rejected"}, 1)
+		p.serf.logger.Printf("[TRACE] serf: Rejected coordinate from %s: %v\n",
 			other.Name, err)
 		return
 	}
diff --git a/vendor/vendor.json b/vendor/vendor.json
index d6f3d4acb..f125b198c 100644
--- a/vendor/vendor.json
+++ b/vendor/vendor.json
@@ -63,8 +63,8 @@
 		{"path":"github.com/hashicorp/net-rpc-msgpackrpc","checksumSHA1":"qnlqWJYV81ENr61SZk9c65R1mDo=","revision":"a14192a58a694c123d8fe5481d4a4727d6ae82f3","revisionTime":"2015-11-16T02:03:38Z"},
 		{"path":"github.com/hashicorp/raft","checksumSHA1":"JjJtGJi1ywWhVhs/PvTXxe4TeD8=","revision":"6d14f0c70869faabd9e60ba7ed88a6cbbd6a661f","revisionTime":"2017-10-03T22:09:13Z","version":"v1.0.0","versionExact":"v1.0.0"},
 		{"path":"github.com/hashicorp/raft-boltdb","checksumSHA1":"QAxukkv54/iIvLfsUP6IK4R0m/A=","revision":"d1e82c1ec3f15ee991f7cc7ffd5b67ff6f5bbaee","revisionTime":"2015-02-01T20:08:39Z"},
-		{"path":"github.com/hashicorp/serf/coordinate","checksumSHA1":"mS15CkImPzXYsgNwl3Mt9Gh3Vb0=","comment":"v0.7.0-66-g6c4672d","revision":"c20a0b1b1ea9eb8168bcdec0116688fa9254e449","revisionTime":"2017-10-22T02:00:50Z"},
-		{"path":"github.com/hashicorp/serf/serf","checksumSHA1":"NegZzEwYOlfkbvy+jTBkX3OBcRM=","comment":"v0.7.0-66-g6c4672d","revision":"a110af454b635c75adc2b7eee541af2c68666d97","revisionTime":"2017-12-07T01:04:04Z"},
+		{"path":"github.com/hashicorp/serf/coordinate","checksumSHA1":"0PeWsO2aI+2PgVYlYlDPKfzCLEQ=","comment":"v0.7.0-66-g6c4672d","revision":"b6017ae61f4420ed0c02d5eeeb9ff3fc02953f14","revisionTime":"2018-01-19T22:43:00Z"},
+		{"path":"github.com/hashicorp/serf/serf","checksumSHA1":"QGImnWfhk0ILLZszcf3vRs/Ft7g=","comment":"v0.7.0-66-g6c4672d","revision":"b6017ae61f4420ed0c02d5eeeb9ff3fc02953f14","revisionTime":"2018-01-19T22:43:00Z"},
 		{"path":"github.com/hashicorp/yamux","checksumSHA1":"ZhK6IO2XN81Y+3RAjTcVm1Ic7oU=","revision":"d1caa6c97c9fc1cc9e83bbe34d0603f9ff0ce8bd","revisionTime":"2016-07-20T23:31:40Z"},
 		{"path":"github.com/mattn/go-isatty","checksumSHA1":"xZuhljnmBysJPta/lMyYmJdujCg=","revision":"66b8e73f3f5cda9f96b69efd03dd3d7fc4a5cdb8","revisionTime":"2016-08-06T12:27:52Z"},
 		{"path":"github.com/miekg/dns","checksumSHA1":"Jo+pItYOocIRdoFL0fc4nHhUEJY=","revision":"bbca4873b326f5dc54bfe31148446d4ed79a5a02","revisionTime":"2017-08-08T22:19:10Z"},