diff --git a/etcdserver/metrics.go b/etcdserver/metrics.go
index 60e5395a3008..670e62a62dc0 100644
--- a/etcdserver/metrics.go
+++ b/etcdserver/metrics.go
@@ -78,6 +78,12 @@ var (
 		Name:      "proposals_failed_total",
 		Help:      "The total number of failed proposals seen.",
 	})
+	readIndexPending = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: "etcd",
+		Subsystem: "server",
+		Name:      "read_indexes_pending_total",
+		Help:      "The total number of pending read indexes not in sync with leader's.",
+	})
 	leaseExpired = prometheus.NewCounter(prometheus.CounterOpts{
 		Namespace: "etcd_debugging",
 		Subsystem: "server",
@@ -109,6 +115,7 @@ func init() {
 	prometheus.MustRegister(proposalsApplied)
 	prometheus.MustRegister(proposalsPending)
 	prometheus.MustRegister(proposalsFailed)
+	prometheus.MustRegister(readIndexPending)
 	prometheus.MustRegister(leaseExpired)
 	prometheus.MustRegister(quotaBackendBytes)
 	prometheus.MustRegister(currentVersion)
diff --git a/etcdserver/v3_server.go b/etcdserver/v3_server.go
index 5826af2fe07f..6598367fdd9c 100644
--- a/etcdserver/v3_server.go
+++ b/etcdserver/v3_server.go
@@ -689,6 +689,7 @@ func (s *EtcdServer) linearizableReadLoop() {
 					} else {
 						plog.Warningf("ignored out-of-date read index response; local node read indexes queueing up and waiting to be in sync with leader (request ID want %d, got %d)", id1, id2)
 					}
+					readIndexPending.Inc()
 				}
 			case <-time.After(s.Cfg.ReqTimeout()):
 				if lg != nil {