diff --git a/expr/func_avgseries.go b/expr/func_avgseries.go
index 78e57d6ebb..10e5b16087 100644
--- a/expr/func_avgseries.go
+++ b/expr/func_avgseries.go
@@ -28,15 +28,9 @@ func (s *FuncAvgSeries) Context(context Context) Context {
 }
 
 func (s *FuncAvgSeries) Exec(cache map[Req][]models.Series) ([]models.Series, error) {
-	var series []models.Series
-	var queryPatts []string
-	for i := range s.in {
-		in, err := s.in[i].Exec(cache)
-		if err != nil {
-			return nil, err
-		}
-		series = append(series, in...)
-		queryPatts = append(queryPatts, in[0].QueryPatt)
+	series, queryPatts, err := consumeFuncs(cache, s.in)
+	if err != nil {
+		return nil, err
 	}
 
 	if len(series) == 0 {
diff --git a/expr/func_persecond.go b/expr/func_persecond.go
index 1ac6cbc746..d18eb76c95 100644
--- a/expr/func_persecond.go
+++ b/expr/func_persecond.go
@@ -32,13 +32,9 @@ func (s *FuncPerSecond) Context(context Context) Context {
 }
 
 func (s *FuncPerSecond) Exec(cache map[Req][]models.Series) ([]models.Series, error) {
-	var series []models.Series
-	for i := range s.in {
-		serie, err := s.in[i].Exec(cache)
-		if err != nil {
-			return nil, err
-		}
-		series = append(series, serie...)
+	series, _, err := consumeFuncs(cache, s.in)
+	if err != nil {
+		return nil, err
 	}
 	maxValue := math.NaN()
 	if s.maxValue > 0 {
diff --git a/expr/func_sumseries.go b/expr/func_sumseries.go
index a2fbabdc7c..1064731ad4 100644
--- a/expr/func_sumseries.go
+++ b/expr/func_sumseries.go
@@ -28,15 +28,9 @@ func (s *FuncSumSeries) Context(context Context) Context {
 }
 
 func (s *FuncSumSeries) Exec(cache map[Req][]models.Series) ([]models.Series, error) {
-	var series []models.Series
-	var queryPatts []string
-	for i := range s.in {
-		in, err := s.in[i].Exec(cache)
-		if err != nil {
-			return nil, err
-		}
-		series = append(series, in...)
-		queryPatts = append(queryPatts, in[0].QueryPatt)
+	series, queryPatts, err := consumeFuncs(cache, s.in)
+	if err != nil {
+		return nil, err
 	}
 
 	if len(series) == 0 {
diff --git a/expr/funcs.go b/expr/funcs.go
index 33dd99cb40..156512dc19 100644
--- a/expr/funcs.go
+++ b/expr/funcs.go
@@ -73,3 +73,19 @@ func summarizeCons(series []models.Series) (consolidation.Consolidator, consolid
 	}
 	return series[0].Consolidator, series[0].QueryCons
 }
+
+func consumeFuncs(cache map[Req][]models.Series, fns []GraphiteFunc) ([]models.Series, []string, error) {
+	var series []models.Series
+	var queryPatts []string
+	for i := range fns {
+		in, err := fns[i].Exec(cache)
+		if err != nil {
+			return nil, nil, err
+		}
+		if len(in) != 0 {
+			series = append(series, in...)
+			queryPatts = append(queryPatts, in[0].QueryPatt)
+		}
+	}
+	return series, queryPatts, nil
+}