diff --git a/.gitignore b/.gitignore
index 3dc9fba6b..5224510fa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,4 +22,5 @@ Gemfile.lock
 /_site
 _site
 *.tmp
-/docs/.jekyll-metadata
\ No newline at end of file
+/docs/.jekyll-metadata
+coverage.txt
\ No newline at end of file
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 36d8ec5c0..877514c67 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -32,6 +32,9 @@ See also [LTS releases](https://docs.victoriametrics.com/lts-releases/).
 * FEATURE: [dashboards](https://grafana.com/orgs/victoriametrics): add [Grafana dashboard](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/dashboards/vmauth.json) and [alerting rules](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/deployment/docker/alerts-vmauth.yml) for [vmauth](https://docs.victoriametrics.com/vmauth/) dashboard. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4313) for details.
 
 * BUGFIX: [docker-compose](https://github.com/VictoriaMetrics/VictoriaMetrics/tree/master/deployment/docker#docker-compose-environment-for-victoriametrics): fix incorrect link to vmui from [VictoriaMetrics plugin in Grafana](https://github.com/VictoriaMetrics/VictoriaMetrics/tree/master/deployment/docker#grafana).
+
+* BUGFIX: [Single-node VictoriaMetrics](https://docs.victoriametrics.com/) and `vmstorage` in [VictoriaMetrics cluster](https://docs.victoriametrics.com/cluster-victoriametrics/): Fix the dateMetricIDCache consistency issue that leads to duplicate per-day index entries when new time series are inserted concurrently. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6534) for details.
+
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix input cursor position reset in modal settings. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/6530).
 
 ## [v1.102.0-rc2](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.102.0-rc2)
diff --git a/lib/storage/storage.go b/lib/storage/storage.go
index 493d7d42a..3e22bb26d 100644
--- a/lib/storage/storage.go
+++ b/lib/storage/storage.go
@@ -2328,16 +2328,28 @@ func (dmc *dateMetricIDCache) SizeBytes() uint64 {
 }
 
 func (dmc *dateMetricIDCache) Has(generation, date, metricID uint64) bool {
+	if byDate := dmc.byDate.Load(); byDate.get(generation, date).Has(metricID) {
+		// Fast path. The majority of calls must go here.
+		return true
+	}
+	// Slow path. Acquire the lock and search the immutable map again and then
+	// also search the mutable map.
+	return dmc.hasSlow(generation, date, metricID)
+}
+
+func (dmc *dateMetricIDCache) hasSlow(generation, date, metricID uint64) bool {
+	dmc.mu.Lock()
+	defer dmc.mu.Unlock()
+
+	// First, check immutable map again because the entry may have been moved to
+	// the immutable map by the time the caller acquires the lock.
 	byDate := dmc.byDate.Load()
 	v := byDate.get(generation, date)
 	if v.Has(metricID) {
-		// Fast path.
-		// The majority of calls must go here.
 		return true
 	}
 
-	// Slow path. Check mutable map.
-	dmc.mu.Lock()
+	// Then check immutable map.
 	vMutable := dmc.byDateMutable.get(generation, date)
 	ok := vMutable.Has(metricID)
 	if ok {
@@ -2348,8 +2360,6 @@ func (dmc *dateMetricIDCache) Has(generation, date, metricID uint64) bool {
 			dmc.slowHits = 0
 		}
 	}
-	dmc.mu.Unlock()
-
 	return ok
 }
 
diff --git a/lib/storage/storage_test.go b/lib/storage/storage_test.go
index 6763ba9d4..7ce8fa30d 100644
--- a/lib/storage/storage_test.go
+++ b/lib/storage/storage_test.go
@@ -8,6 +8,7 @@ import (
 	"reflect"
 	"sort"
 	"strings"
+	"sync"
 	"testing"
 	"testing/quick"
 	"time"
@@ -156,6 +157,30 @@ func testDateMetricIDCache(c *dateMetricIDCache, concurrent bool) error {
 	return nil
 }
 
+func TestDateMetricIDCacheIsConsistent(_ *testing.T) {
+	const (
+		generation  = 1
+		date        = 1
+		concurrency = 2
+		numMetrics  = 100000
+	)
+	dmc := newDateMetricIDCache()
+	var wg sync.WaitGroup
+	for i := range concurrency {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for id := uint64(i * numMetrics); id < uint64((i+1)*numMetrics); id++ {
+				dmc.Set(generation, date, id)
+				if !dmc.Has(generation, date, id) {
+					panic(fmt.Errorf("dmc.Has(metricID=%d): unexpected cache miss after adding the entry to cache", id))
+				}
+			}
+		}()
+	}
+	wg.Wait()
+}
+
 func TestUpdateCurrHourMetricIDs(t *testing.T) {
 	newStorage := func() *Storage {
 		var s Storage