diff --git a/app/vmselect/netstorage/netstorage.go b/app/vmselect/netstorage/netstorage.go
index b6fb194491..d382822efa 100644
--- a/app/vmselect/netstorage/netstorage.go
+++ b/app/vmselect/netstorage/netstorage.go
@@ -1139,30 +1139,6 @@ func newTmpBlocksFileWrapper() *tmpBlocksFileWrapper {
 	}
 }
 
-func (tbfw *tmpBlocksFileWrapper) Finalize() ([]string, map[string][]tmpBlockAddr, uint64, error) {
-	var bytesTotal uint64
-	for i, tbf := range tbfw.tbfs {
-		if err := tbf.Finalize(); err != nil {
-			// Close the remaining tbfs before returning the error
-			closeTmpBlockFiles(tbfw.tbfs[i:])
-			return nil, nil, 0, fmt.Errorf("cannot finalize temporary blocks file with %d series: %w", len(tbfw.ms[i]), err)
-		}
-		bytesTotal += tbf.Len()
-	}
-	orderedMetricNames := tbfw.orderedMetricNamess[0]
-	addrsByMetricName := make(map[string][]tmpBlockAddr)
-	for i, m := range tbfw.ms {
-		for _, metricName := range tbfw.orderedMetricNamess[i] {
-			dstAddrs, ok := addrsByMetricName[metricName]
-			if !ok {
-				orderedMetricNames = append(orderedMetricNames, metricName)
-			}
-			addrsByMetricName[metricName] = append(dstAddrs, m[metricName]...)
-		}
-	}
-	return orderedMetricNames, addrsByMetricName, bytesTotal, nil
-}
-
 func (tbfw *tmpBlocksFileWrapper) RegisterAndWriteBlock(mb *storage.MetricBlock, workerIdx int) error {
 	bb := tmpBufPool.Get()
 	bb.B = storage.MarshalBlock(bb.B[:0], &mb.Block)
@@ -1180,13 +1156,38 @@ func (tbfw *tmpBlocksFileWrapper) RegisterAndWriteBlock(mb *storage.MetricBlock,
 	} else {
 		// An optimization for big number of time series with long names: store only a single copy of metricNameStr
 		// in both tbfw.orderedMetricNamess and tbfw.ms.
-		tbfw.orderedMetricNamess[workerIdx] = append(tbfw.orderedMetricNamess[workerIdx], string(metricName))
-		metricNameStr := tbfw.orderedMetricNamess[workerIdx][len(tbfw.orderedMetricNamess[workerIdx])-1]
+		orderedMetricNames := tbfw.orderedMetricNamess[workerIdx]
+		orderedMetricNames = append(orderedMetricNames, string(metricName))
+		metricNameStr := orderedMetricNames[len(orderedMetricNames)-1]
 		m[metricNameStr] = addrs
+		tbfw.orderedMetricNamess[workerIdx] = orderedMetricNames
 	}
 	return nil
 }
 
+func (tbfw *tmpBlocksFileWrapper) Finalize() ([]string, map[string][]tmpBlockAddr, uint64, error) {
+	var bytesTotal uint64
+	for i, tbf := range tbfw.tbfs {
+		if err := tbf.Finalize(); err != nil {
+			closeTmpBlockFiles(tbfw.tbfs)
+			return nil, nil, 0, fmt.Errorf("cannot finalize temporary blocks file with %d series: %w", len(tbfw.ms[i]), err)
+		}
+		bytesTotal += tbf.Len()
+	}
+	orderedMetricNames := tbfw.orderedMetricNamess[0]
+	addrsByMetricName := tbfw.ms[0]
+	for i, m := range tbfw.ms[1:] {
+		for _, metricName := range tbfw.orderedMetricNamess[i] {
+			dstAddrs, ok := addrsByMetricName[metricName]
+			if !ok {
+				orderedMetricNames = append(orderedMetricNames, metricName)
+			}
+			addrsByMetricName[metricName] = append(dstAddrs, m[metricName]...)
+		}
+	}
+	return orderedMetricNames, addrsByMetricName, bytesTotal, nil
+}
+
 var metricNamePool = &sync.Pool{
 	New: func() interface{} {
 		return &storage.MetricName{}