diff --git a/app/vmselect/promql/exec.go b/app/vmselect/promql/exec.go
index ab2753fc8..7959cf169 100644
--- a/app/vmselect/promql/exec.go
+++ b/app/vmselect/promql/exec.go
@@ -12,6 +12,7 @@ import (
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/netstorage"
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/querystats"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/decimal"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/querytracer"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
@@ -121,10 +122,11 @@ func timeseriesToResult(tss []*timeseries, maySort bool) ([]netstorage.Result, e
 	bb := bbPool.Get()
 	for i, ts := range tss {
 		bb.B = marshalMetricNameSorted(bb.B[:0], &ts.MetricName)
-		if _, ok := m[string(bb.B)]; ok {
+		k := bytesutil.InternBytes(bb.B)
+		if _, ok := m[k]; ok {
 			return nil, fmt.Errorf(`duplicate output timeseries: %s`, stringMetricName(&ts.MetricName))
 		}
-		m[string(bb.B)] = struct{}{}
+		m[k] = struct{}{}
 
 		rs := &result[i]
 		rs.MetricName.CopyFrom(&ts.MetricName)