diff --git a/web/api/v1/api_test.go b/web/api/v1/api_test.go
index 321a13d5e..99e3b292e 100644
--- a/web/api/v1/api_test.go
+++ b/web/api/v1/api_test.go
@@ -3417,27 +3417,57 @@ func TestReturnAPIError(t *testing.T) {
 var testResponseWriter = httptest.ResponseRecorder{}
 
 func BenchmarkRespond(b *testing.B) {
-	b.ReportAllocs()
-	request, err := http.NewRequest(http.MethodGet, "/does-not-matter", nil)
-	require.NoError(b, err)
 	points := []promql.FPoint{}
 	for i := 0; i < 10000; i++ {
 		points = append(points, promql.FPoint{F: float64(i * 1000000), T: int64(i)})
 	}
-	response := &QueryData{
-		ResultType: parser.ValueTypeMatrix,
-		Result: promql.Matrix{
-			promql.Series{
-				Floats: points,
-				Metric: labels.EmptyLabels(),
-			},
-		},
+	matrix := promql.Matrix{}
+	for i := 0; i < 1000; i++ {
+		matrix = append(matrix, promql.Series{
+			Metric: labels.FromStrings("__name__", fmt.Sprintf("series%v", i),
+				"label", fmt.Sprintf("series%v", i),
+				"label2", fmt.Sprintf("series%v", i)),
+			Floats: points[:10],
+		})
 	}
-	b.ResetTimer()
-	api := API{}
-	api.InstallCodec(JSONCodec{})
-	for n := 0; n < b.N; n++ {
-		api.respond(&testResponseWriter, request, response, nil)
+	series := []labels.Labels{}
+	for i := 0; i < 1000; i++ {
+		series = append(series, labels.FromStrings("__name__", fmt.Sprintf("series%v", i),
+			"label", fmt.Sprintf("series%v", i),
+			"label2", fmt.Sprintf("series%v", i)))
+	}
+
+	cases := []struct {
+		name     string
+		response interface{}
+	}{
+		{name: "10000 points no labels", response: &QueryData{
+			ResultType: parser.ValueTypeMatrix,
+			Result: promql.Matrix{
+				promql.Series{
+					Floats: points,
+					Metric: labels.EmptyLabels(),
+				},
+			},
+		}},
+		{name: "1000 labels", response: series},
+		{name: "1000 series 10 points", response: &QueryData{
+			ResultType: parser.ValueTypeMatrix,
+			Result:     matrix,
+		}},
+	}
+	for _, c := range cases {
+		b.Run(c.name, func(b *testing.B) {
+			b.ReportAllocs()
+			request, err := http.NewRequest(http.MethodGet, "/does-not-matter", nil)
+			require.NoError(b, err)
+			b.ResetTimer()
+			api := API{}
+			api.InstallCodec(JSONCodec{})
+			for n := 0; n < b.N; n++ {
+				api.respond(&testResponseWriter, request, c.response, nil)
+			}
+		})
 	}
 }
 
diff --git a/web/api/v1/json_codec.go b/web/api/v1/json_codec.go
index 62e7563b1..f1a8104cc 100644
--- a/web/api/v1/json_codec.go
+++ b/web/api/v1/json_codec.go
@@ -19,6 +19,7 @@ import (
 	jsoniter "github.com/json-iterator/go"
 
 	"github.com/prometheus/prometheus/model/exemplar"
+	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/util/jsonutil"
 )
@@ -29,6 +30,7 @@ func init() {
 	jsoniter.RegisterTypeEncoderFunc("promql.FPoint", marshalFPointJSON, marshalPointJSONIsEmpty)
 	jsoniter.RegisterTypeEncoderFunc("promql.HPoint", marshalHPointJSON, marshalPointJSONIsEmpty)
 	jsoniter.RegisterTypeEncoderFunc("exemplar.Exemplar", marshalExemplarJSON, marshalExemplarJSONEmpty)
+	jsoniter.RegisterTypeEncoderFunc("labels.Labels", unsafeMarshalLabelsJSON, labelsIsEmpty)
 }
 
 // JSONCodec is a Codec that encodes API responses as JSON.
@@ -68,12 +70,7 @@ func marshalSeriesJSON(ptr unsafe.Pointer, stream *jsoniter.Stream) {
 	s := *((*promql.Series)(ptr))
 	stream.WriteObjectStart()
 	stream.WriteObjectField(`metric`)
-	m, err := s.Metric.MarshalJSON()
-	if err != nil {
-		stream.Error = err
-		return
-	}
-	stream.SetBuffer(append(stream.Buffer(), m...))
+	marshalLabelsJSON(s.Metric, stream)
 
 	for i, p := range s.Floats {
 		stream.WriteMore()
@@ -129,12 +126,7 @@ func marshalSampleJSON(ptr unsafe.Pointer, stream *jsoniter.Stream) {
 	s := *((*promql.Sample)(ptr))
 	stream.WriteObjectStart()
 	stream.WriteObjectField(`metric`)
-	m, err := s.Metric.MarshalJSON()
-	if err != nil {
-		stream.Error = err
-		return
-	}
-	stream.SetBuffer(append(stream.Buffer(), m...))
+	marshalLabelsJSON(s.Metric, stream)
 	stream.WriteMore()
 	if s.H == nil {
 		stream.WriteObjectField(`value`)
@@ -194,12 +186,7 @@ func marshalExemplarJSON(ptr unsafe.Pointer, stream *jsoniter.Stream) {
 
 	// "labels" key.
 	stream.WriteObjectField(`labels`)
-	lbls, err := p.Labels.MarshalJSON()
-	if err != nil {
-		stream.Error = err
-		return
-	}
-	stream.SetBuffer(append(stream.Buffer(), lbls...))
+	marshalLabelsJSON(p.Labels, stream)
 
 	// "value" key.
 	stream.WriteMore()
@@ -217,3 +204,28 @@ func marshalExemplarJSON(ptr unsafe.Pointer, stream *jsoniter.Stream) {
 func marshalExemplarJSONEmpty(unsafe.Pointer) bool {
 	return false
 }
+
+func unsafeMarshalLabelsJSON(ptr unsafe.Pointer, stream *jsoniter.Stream) {
+	labelsPtr := (*labels.Labels)(ptr)
+	marshalLabelsJSON(*labelsPtr, stream)
+}
+
+func marshalLabelsJSON(lbls labels.Labels, stream *jsoniter.Stream) {
+	stream.WriteObjectStart()
+	i := 0
+	lbls.Range(func(v labels.Label) {
+		if i != 0 {
+			stream.WriteMore()
+		}
+		i++
+		stream.WriteString(v.Name)
+		stream.WriteRaw(`:`)
+		stream.WriteString(v.Value)
+	})
+	stream.WriteObjectEnd()
+}
+
+func labelsIsEmpty(ptr unsafe.Pointer) bool {
+	labelsPtr := (*labels.Labels)(ptr)
+	return labelsPtr.IsEmpty()
+}