diff --git a/api/prometheus/v1/api.go b/api/prometheus/v1/api.go
index c081bc8..5fde717 100644
--- a/api/prometheus/v1/api.go
+++ b/api/prometheus/v1/api.go
@@ -229,9 +229,9 @@ type API interface {
 	// Flags returns the flag values that Prometheus was launched with.
 	Flags(ctx context.Context) (FlagsResult, error)
 	// LabelNames returns all the unique label names present in the block in sorted order.
-	LabelNames(ctx context.Context) ([]string, error)
+	LabelNames(ctx context.Context) ([]string, api.Warnings, error)
 	// LabelValues performs a query for the values of the given label.
-	LabelValues(ctx context.Context, label string) (model.LabelValues, error)
+	LabelValues(ctx context.Context, label string) (model.LabelValues, api.Warnings, error)
 	// Query performs a query for the given time.
 	Query(ctx context.Context, query string, ts time.Time) (model.Value, api.Warnings, error)
 	// QueryRange performs a query for the given range.
@@ -625,32 +625,32 @@ func (h *httpAPI) Flags(ctx context.Context) (FlagsResult, error) {
 	return res, json.Unmarshal(body, &res)
 }
 
-func (h *httpAPI) LabelNames(ctx context.Context) ([]string, error) {
+func (h *httpAPI) LabelNames(ctx context.Context) ([]string, api.Warnings, error) {
 	u := h.client.URL(epLabels, nil)
 	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
-	_, body, _, err := h.client.Do(ctx, req)
+	_, body, w, err := h.client.Do(ctx, req)
 	if err != nil {
-		return nil, err
+		return nil, w, err
 	}
 	var labelNames []string
-	return labelNames, json.Unmarshal(body, &labelNames)
+	return labelNames, w, json.Unmarshal(body, &labelNames)
 }
 
-func (h *httpAPI) LabelValues(ctx context.Context, label string) (model.LabelValues, error) {
+func (h *httpAPI) LabelValues(ctx context.Context, label string) (model.LabelValues, api.Warnings, error) {
 	u := h.client.URL(epLabelValues, map[string]string{"name": label})
 	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
-	_, body, _, err := h.client.Do(ctx, req)
+	_, body, w, err := h.client.Do(ctx, req)
 	if err != nil {
-		return nil, err
+		return nil, w, err
 	}
 	var labelValues model.LabelValues
-	return labelValues, json.Unmarshal(body, &labelValues)
+	return labelValues, w, json.Unmarshal(body, &labelValues)
 }
 
 func (h *httpAPI) Query(ctx context.Context, query string, ts time.Time) (model.Value, api.Warnings, error) {
diff --git a/api/prometheus/v1/api_test.go b/api/prometheus/v1/api_test.go
index 28e7214..0572f86 100644
--- a/api/prometheus/v1/api_test.go
+++ b/api/prometheus/v1/api_test.go
@@ -137,15 +137,13 @@ func TestAPIs(t *testing.T) {
 
 	doLabelNames := func(label string) func() (interface{}, api.Warnings, error) {
 		return func() (interface{}, api.Warnings, error) {
-			v, err := promAPI.LabelNames(context.Background())
-			return v, nil, err
+			return promAPI.LabelNames(context.Background())
 		}
 	}
 
 	doLabelValues := func(label string) func() (interface{}, api.Warnings, error) {
 		return func() (interface{}, api.Warnings, error) {
-			v, err := promAPI.LabelValues(context.Background(), label)
-			return v, nil, err
+			return promAPI.LabelValues(context.Background(), label)
 		}
 	}
 
@@ -337,6 +335,15 @@ func TestAPIs(t *testing.T) {
 			reqPath:   "/api/v1/labels",
 			res:       []string{"val1", "val2"},
 		},
+		{
+			do:         doLabelNames("mylabel"),
+			inRes:      []string{"val1", "val2"},
+			inWarnings: []string{"a"},
+			reqMethod:  "GET",
+			reqPath:    "/api/v1/labels",
+			res:        []string{"val1", "val2"},
+			warnings:   []string{"a"},
+		},
 
 		{
 			do:        doLabelNames("mylabel"),
@@ -345,6 +352,15 @@ func TestAPIs(t *testing.T) {
 			reqPath:   "/api/v1/labels",
 			err:       fmt.Errorf("some error"),
 		},
+		{
+			do:         doLabelNames("mylabel"),
+			inErr:      fmt.Errorf("some error"),
+			inWarnings: []string{"a"},
+			reqMethod:  "GET",
+			reqPath:    "/api/v1/labels",
+			err:        fmt.Errorf("some error"),
+			warnings:   []string{"a"},
+		},
 
 		{
 			do:        doLabelValues("mylabel"),
@@ -353,6 +369,15 @@ func TestAPIs(t *testing.T) {
 			reqPath:   "/api/v1/label/mylabel/values",
 			res:       model.LabelValues{"val1", "val2"},
 		},
+		{
+			do:         doLabelValues("mylabel"),
+			inRes:      []string{"val1", "val2"},
+			inWarnings: []string{"a"},
+			reqMethod:  "GET",
+			reqPath:    "/api/v1/label/mylabel/values",
+			res:        model.LabelValues{"val1", "val2"},
+			warnings:   []string{"a"},
+		},
 
 		{
 			do:        doLabelValues("mylabel"),
@@ -361,6 +386,15 @@ func TestAPIs(t *testing.T) {
 			reqPath:   "/api/v1/label/mylabel/values",
 			err:       fmt.Errorf("some error"),
 		},
+		{
+			do:         doLabelValues("mylabel"),
+			inErr:      fmt.Errorf("some error"),
+			inWarnings: []string{"a"},
+			reqMethod:  "GET",
+			reqPath:    "/api/v1/label/mylabel/values",
+			err:        fmt.Errorf("some error"),
+			warnings:   []string{"a"},
+		},
 
 		{
 			do: doSeries("up", testTime.Add(-time.Minute), testTime),