diff --git a/promql/engine.go b/promql/engine.go
index 2e5f620e3..5fb1d849d 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -1311,7 +1311,6 @@ func (ev *evaluator) rangeEvalAgg(aggExpr *parser.AggregateExpr, sortedGrouping
 	// Keep a copy of the original point slice so that it can be returned to the pool.
 	origMatrix := inputMatrix
 
-	var vector Vector // Input vectors for the function.
 	biggestLen := len(inputMatrix)
 	enh := &EvalNodeHelper{}
 	seriess := make(map[uint64]Series, biggestLen) // Output series by series hash.
@@ -1321,7 +1320,6 @@ func (ev *evaluator) rangeEvalAgg(aggExpr *parser.AggregateExpr, sortedGrouping
 	buf := make([]byte, 0, 1024)
 
 	seriesHelper := make([]EvalSeriesHelper, len(inputMatrix))
-	bufHelper := make([]EvalSeriesHelper, len(inputMatrix))
 
 	for si, series := range inputMatrix {
 		seriesHelper[si].groupingKey, buf = generateGroupingKey(series.Metric, sortedGrouping, aggExpr.Without, buf)
@@ -1333,36 +1331,10 @@ func (ev *evaluator) rangeEvalAgg(aggExpr *parser.AggregateExpr, sortedGrouping
 		}
 		// Reset number of samples in memory after each timestamp.
 		ev.currentSamples = tempNumSamples
-		// Gather input vectors for this timestamp.
-		{
-			vector = vector[:0]
-			bufHelper = bufHelper[:0]
-
-			for si, series := range inputMatrix {
-				switch {
-				case len(series.Floats) > 0 && series.Floats[0].T == ts:
-					vector = append(vector, Sample{Metric: series.Metric, F: series.Floats[0].F, T: ts})
-					// Move input vectors forward so we don't have to re-scan the same
-					// past points at the next step.
-					inputMatrix[si].Floats = series.Floats[1:]
-				case len(series.Histograms) > 0 && series.Histograms[0].T == ts:
-					vector = append(vector, Sample{Metric: series.Metric, H: series.Histograms[0].H, T: ts})
-					inputMatrix[si].Histograms = series.Histograms[1:]
-				default:
-					continue
-				}
-				bufHelper = append(bufHelper, seriesHelper[si])
-				ev.currentSamples++
-				if ev.currentSamples > ev.maxSamples {
-					ev.error(ErrTooManySamples(env))
-				}
-			}
-			ev.samplesStats.UpdatePeak(ev.currentSamples)
-		}
 
 		// Make the function call.
 		enh.Ts = ts
-		result, ws := ev.aggregation(aggExpr, sortedGrouping, param, vector, bufHelper, enh, seriess)
+		result, ws := ev.aggregation(aggExpr, sortedGrouping, param, inputMatrix, seriesHelper, enh, seriess)
 
 		warnings.Merge(ws)
 
@@ -2726,7 +2698,7 @@ type groupedAggregation struct {
 
 // aggregation evaluates an aggregation operation on a Vector. The provided grouping labels
 // must be sorted.
-func (ev *evaluator) aggregation(e *parser.AggregateExpr, grouping []string, param interface{}, vec Vector, seriesHelper []EvalSeriesHelper, enh *EvalNodeHelper, seriess map[uint64]Series) (Matrix, annotations.Annotations) {
+func (ev *evaluator) aggregation(e *parser.AggregateExpr, grouping []string, param interface{}, inputMatrix Matrix, seriesHelper []EvalSeriesHelper, enh *EvalNodeHelper, seriess map[uint64]Series) (Matrix, annotations.Annotations) {
 	op := e.Op
 	without := e.Without
 	var annos annotations.Annotations
@@ -2748,7 +2720,26 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, grouping []string, par
 		q = param.(float64)
 	}
 
-	for si, s := range vec {
+	for si, series := range inputMatrix {
+		var s Sample
+
+		switch {
+		case len(series.Floats) > 0 && series.Floats[0].T == enh.Ts:
+			s = Sample{Metric: series.Metric, F: series.Floats[0].F, T: enh.Ts}
+			// Move input vectors forward so we don't have to re-scan the same
+			// past points at the next step.
+			inputMatrix[si].Floats = series.Floats[1:]
+		case len(series.Histograms) > 0 && series.Histograms[0].T == enh.Ts:
+			s = Sample{Metric: series.Metric, H: series.Histograms[0].H, T: enh.Ts}
+			inputMatrix[si].Histograms = series.Histograms[1:]
+		default:
+			continue
+		}
+		ev.currentSamples++
+		if ev.currentSamples > ev.maxSamples {
+			ev.error(ErrTooManySamples(env))
+		}
+
 		metric := s.Metric
 		groupingKey := seriesHelper[si].groupingKey
 
@@ -2775,7 +2766,7 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, grouping []string, par
 				newAgg.groupCount = 0
 			}
 
-			inputVecLen := int64(len(vec))
+			inputVecLen := int64(len(inputMatrix))
 			resultSize := k
 			switch {
 			case k > inputVecLen: