diff --git a/promql/engine.go b/promql/engine.go
index a6fc29540..fd2022207 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -2360,15 +2360,14 @@ func (ev *evaluator) aggregation(op parser.ItemType, grouping []string, without
 		}
 	}
 
-	lb := labels.NewBuilder(labels.EmptyLabels())
 	var buf []byte
 	for si, s := range vec {
 		metric := s.Metric
 
 		if op == parser.COUNT_VALUES {
-			lb.Reset(metric)
-			lb.Set(valueLabel, strconv.FormatFloat(s.V, 'f', -1, 64))
-			metric = lb.Labels(labels.EmptyLabels())
+			enh.resetBuilder(metric)
+			enh.lb.Set(valueLabel, strconv.FormatFloat(s.V, 'f', -1, 64))
+			metric = enh.lb.Labels(labels.EmptyLabels())
 
 			// We've changed the metric so we have to recompute the grouping key.
 			recomputeGroupingKey = true
@@ -2385,14 +2384,14 @@ func (ev *evaluator) aggregation(op parser.ItemType, grouping []string, without
 		group, ok := result[groupingKey]
 		// Add a new group if it doesn't exist.
 		if !ok {
-			lb.Reset(metric)
+			enh.resetBuilder(metric)
 			if without {
-				lb.Del(grouping...)
-				lb.Del(labels.MetricName)
+				enh.lb.Del(grouping...)
+				enh.lb.Del(labels.MetricName)
 			} else {
-				lb.Keep(grouping...)
+				enh.lb.Keep(grouping...)
 			}
-			m := lb.Labels(labels.EmptyLabels())
+			m := enh.lb.Labels(labels.EmptyLabels())
 			newAgg := &groupedAggregation{
 				labels:     m,
 				value:      s.V,