diff --git a/promql/bench.go b/promql/bench.go
index a60091e31..b628aa2a8 100644
--- a/promql/bench.go
+++ b/promql/bench.go
@@ -39,7 +39,9 @@ func (b *Benchmark) Run() {
 	b.b.ReportAllocs()
 	b.b.ResetTimer()
 	for i := 0; i < b.b.N; i++ {
-		b.t.RunAsBenchmark(b)
+		if err := b.t.RunAsBenchmark(b); err != nil {
+			b.b.Error(err)
+		}
 		b.iterCount++
 	}
 }
diff --git a/promql/engine.go b/promql/engine.go
index bb566850e..d9c33d413 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -481,41 +481,31 @@ func (ng *Engine) populateIterators(s *EvalStmt) error {
 	Inspect(s.Expr, func(node Node) bool {
 		switch n := node.(type) {
 		case *VectorSelector:
-			var iterators []local.SeriesIterator
-			var err error
 			if s.Start.Equal(s.End) {
-				iterators, err = ng.querier.QueryInstant(
+				n.iterators, queryErr = ng.querier.QueryInstant(
 					s.Start.Add(-n.Offset),
 					StalenessDelta,
 					n.LabelMatchers...,
 				)
 			} else {
-				iterators, err = ng.querier.QueryRange(
+				n.iterators, queryErr = ng.querier.QueryRange(
 					s.Start.Add(-n.Offset-StalenessDelta),
 					s.End.Add(-n.Offset),
 					n.LabelMatchers...,
 				)
 			}
-			if err != nil {
-				queryErr = err
+			if queryErr != nil {
 				return false
 			}
-			for _, it := range iterators {
-				n.iterators = append(n.iterators, it)
-			}
 		case *MatrixSelector:
-			iterators, err := ng.querier.QueryRange(
+			n.iterators, queryErr = ng.querier.QueryRange(
 				s.Start.Add(-n.Offset-n.Range),
 				s.End.Add(-n.Offset),
 				n.LabelMatchers...,
 			)
-			if err != nil {
-				queryErr = err
+			if queryErr != nil {
 				return false
 			}
-			for _, it := range iterators {
-				n.iterators = append(n.iterators, it)
-			}
 		}
 		return true
 	})
diff --git a/promql/functions.go b/promql/functions.go
index e4d896e23..9e49dc360 100644
--- a/promql/functions.go
+++ b/promql/functions.go
@@ -522,7 +522,7 @@ func funcStddevOverTime(ev *evaluator, args Expressions) model.Value {
 		for _, v := range values {
 			sum += v.Value
 			squaredSum += v.Value * v.Value
-			count += 1
+			count++
 		}
 		avg := sum / count
 		return model.SampleValue(math.Sqrt(float64(squaredSum/count - avg*avg)))
@@ -536,7 +536,7 @@ func funcStdvarOverTime(ev *evaluator, args Expressions) model.Value {
 		for _, v := range values {
 			sum += v.Value
 			squaredSum += v.Value * v.Value
-			count += 1
+			count++
 		}
 		avg := sum / count
 		return squaredSum/count - avg*avg
diff --git a/promql/functions_test.go b/promql/functions_test.go
index bbb51df37..41a5d3216 100644
--- a/promql/functions_test.go
+++ b/promql/functions_test.go
@@ -22,7 +22,7 @@ load 5m
     http_requests{path="/foo"}    0+10x8064
 
 eval instant at 4w holt_winters(http_requests[4w], 0.3, 0.3)
-    {path="/foo"} 20160
+    {path="/foo"} 80640
 `
 
 	bench := NewBenchmark(b, input)
@@ -51,7 +51,7 @@ load 1m
     http_requests{path="/foo"}    0+10x1440
 
 eval instant at 1d holt_winters(http_requests[1d], 0.3, 0.3)
-    {path="/foo"} 20160
+    {path="/foo"} 14400
 `
 
 	bench := NewBenchmark(b, input)
@@ -65,7 +65,7 @@ load 1m
     http_requests{path="/foo"}    0+10x1440
 
 eval instant at 1d changes(http_requests[1d])
-    {path="/foo"} 20160
+    {path="/foo"} 1440
 `
 
 	bench := NewBenchmark(b, input)