diff --git a/tsdb/agent/db.go b/tsdb/agent/db.go
index 7d42d14fe..a06d8f1f9 100644
--- a/tsdb/agent/db.go
+++ b/tsdb/agent/db.go
@@ -392,7 +392,7 @@ func (db *DB) replayWAL() error {
 func (db *DB) loadWAL(r *wal.Reader, multiRef map[chunks.HeadSeriesRef]chunks.HeadSeriesRef) (err error) {
 	var (
 		dec     record.Decoder
-		lastRef chunks.HeadSeriesRef
+		lastRef = chunks.HeadSeriesRef(db.nextRef.Load())
 
 		decoded    = make(chan interface{}, 10)
 		errCh      = make(chan error, 1)
diff --git a/tsdb/agent/db_test.go b/tsdb/agent/db_test.go
index e99712f71..a44b6c728 100644
--- a/tsdb/agent/db_test.go
+++ b/tsdb/agent/db_test.go
@@ -15,6 +15,7 @@ package agent
 
 import (
 	"context"
+	"fmt"
 	"path/filepath"
 	"strconv"
 	"testing"
@@ -24,6 +25,7 @@ import (
 
 	"github.com/prometheus/client_golang/prometheus"
 	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 
 	"github.com/prometheus/prometheus/model/exemplar"
@@ -409,6 +411,41 @@ func TestLockfile(t *testing.T) {
 	})
 }
 
+func Test_ExistingWAL_NextRef(t *testing.T) {
+	dbDir := t.TempDir()
+	rs := remote.NewStorage(log.NewNopLogger(), nil, startTime, dbDir, time.Second*30, nil)
+	defer func() {
+		require.NoError(t, rs.Close())
+	}()
+
+	db, err := Open(log.NewNopLogger(), nil, rs, dbDir, DefaultOptions())
+	require.NoError(t, err)
+
+	seriesCount := 10
+
+	// Append <seriesCount> series
+	app := db.Appender(context.Background())
+	for i := 0; i < seriesCount; i++ {
+		lset := labels.Labels{
+			{Name: model.MetricNameLabel, Value: fmt.Sprintf("series_%d", i)},
+		}
+		_, err := app.Append(0, lset, 0, 100)
+		require.NoError(t, err)
+	}
+	require.NoError(t, app.Commit())
+
+	// Truncate the WAL to force creation of a new segment.
+	require.NoError(t, db.truncate(0))
+	require.NoError(t, db.Close())
+
+	// Create a new storage and see what nextRef is initialized to.
+	db, err = Open(log.NewNopLogger(), nil, rs, dbDir, DefaultOptions())
+	require.NoError(t, err)
+	defer require.NoError(t, db.Close())
+
+	require.Equal(t, uint64(seriesCount), db.nextRef.Load(), "nextRef should be equal to the number of series written across the entire WAL")
+}
+
 func startTime() (int64, error) {
 	return time.Now().Unix() * 1000, nil
 }