diff --git a/api/prometheus/v1/api.go b/api/prometheus/v1/api.go
index 77e7348..c081bc8 100644
--- a/api/prometheus/v1/api.go
+++ b/api/prometheus/v1/api.go
@@ -237,7 +237,7 @@ type API interface {
 	// QueryRange performs a query for the given range.
 	QueryRange(ctx context.Context, query string, r Range) (model.Value, api.Warnings, error)
 	// Series finds series by label matchers.
-	Series(ctx context.Context, matches []string, startTime time.Time, endTime time.Time) ([]model.LabelSet, error)
+	Series(ctx context.Context, matches []string, startTime time.Time, endTime time.Time) ([]model.LabelSet, api.Warnings, error)
 	// Snapshot creates a snapshot of all current data into snapshots/<datetime>-<rand>
 	// under the TSDB's data directory and returns the directory as response.
 	Snapshot(ctx context.Context, skipHead bool) (SnapshotResult, error)
@@ -696,7 +696,7 @@ func (h *httpAPI) QueryRange(ctx context.Context, query string, r Range) (model.
 	return model.Value(qres.v), warnings, json.Unmarshal(body, &qres)
 }
 
-func (h *httpAPI) Series(ctx context.Context, matches []string, startTime time.Time, endTime time.Time) ([]model.LabelSet, error) {
+func (h *httpAPI) Series(ctx context.Context, matches []string, startTime time.Time, endTime time.Time) ([]model.LabelSet, api.Warnings, error) {
 	u := h.client.URL(epSeries, nil)
 	q := u.Query()
 
@@ -711,16 +711,16 @@ func (h *httpAPI) Series(ctx context.Context, matches []string, startTime time.T
 
 	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, warnings, err := h.client.Do(ctx, req)
 	if err != nil {
-		return nil, err
+		return nil, warnings, err
 	}
 
 	var mset []model.LabelSet
-	return mset, json.Unmarshal(body, &mset)
+	return mset, warnings, json.Unmarshal(body, &mset)
 }
 
 func (h *httpAPI) Snapshot(ctx context.Context, skipHead bool) (SnapshotResult, error) {
diff --git a/api/prometheus/v1/api_test.go b/api/prometheus/v1/api_test.go
index f6b4897..28e7214 100644
--- a/api/prometheus/v1/api_test.go
+++ b/api/prometheus/v1/api_test.go
@@ -163,8 +163,7 @@ func TestAPIs(t *testing.T) {
 
 	doSeries := func(matcher string, startTime time.Time, endTime time.Time) func() (interface{}, api.Warnings, error) {
 		return func() (interface{}, api.Warnings, error) {
-			v, err := promAPI.Series(context.Background(), []string{matcher}, startTime, endTime)
-			return v, nil, err
+			return promAPI.Series(context.Background(), []string{matcher}, startTime, endTime)
 		}
 	}
 
@@ -386,6 +385,32 @@ func TestAPIs(t *testing.T) {
 				},
 			},
 		},
+		// Series with data + warning.
+		{
+			do: doSeries("up", testTime.Add(-time.Minute), testTime),
+			inRes: []map[string]string{
+				{
+					"__name__": "up",
+					"job":      "prometheus",
+					"instance": "localhost:9090"},
+			},
+			inWarnings: []string{"a"},
+			reqMethod:  "GET",
+			reqPath:    "/api/v1/series",
+			reqParam: url.Values{
+				"match": []string{"up"},
+				"start": []string{testTime.Add(-time.Minute).Format(time.RFC3339Nano)},
+				"end":   []string{testTime.Format(time.RFC3339Nano)},
+			},
+			res: []model.LabelSet{
+				{
+					"__name__": "up",
+					"job":      "prometheus",
+					"instance": "localhost:9090",
+				},
+			},
+			warnings: []string{"a"},
+		},
 
 		{
 			do:        doSeries("up", testTime.Add(-time.Minute), testTime),
@@ -399,6 +424,21 @@ func TestAPIs(t *testing.T) {
 			},
 			err: fmt.Errorf("some error"),
 		},
+		// Series with error and warning.
+		{
+			do:         doSeries("up", testTime.Add(-time.Minute), testTime),
+			inErr:      fmt.Errorf("some error"),
+			inWarnings: []string{"a"},
+			reqMethod:  "GET",
+			reqPath:    "/api/v1/series",
+			reqParam: url.Values{
+				"match": []string{"up"},
+				"start": []string{testTime.Add(-time.Minute).Format(time.RFC3339Nano)},
+				"end":   []string{testTime.Format(time.RFC3339Nano)},
+			},
+			err:      fmt.Errorf("some error"),
+			warnings: []string{"a"},
+		},
 
 		{
 			do: doSnapshot(true),