diff --git a/api/prometheus/v1/api.go b/api/prometheus/v1/api.go
index b77294778..13b36464d 100644
--- a/api/prometheus/v1/api.go
+++ b/api/prometheus/v1/api.go
@@ -682,6 +682,8 @@ func (h *httpAPI) LabelNames(ctx context.Context, startTime time.Time, endTime t
 	q.Set("start", formatTime(startTime))
 	q.Set("end", formatTime(endTime))
 
+	u.RawQuery = q.Encode()
+
 	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
 	if err != nil {
 		return nil, nil, err
@@ -700,6 +702,8 @@ func (h *httpAPI) LabelValues(ctx context.Context, label string, startTime time.
 	q.Set("start", formatTime(startTime))
 	q.Set("end", formatTime(endTime))
 
+	u.RawQuery = q.Encode()
+
 	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
 	if err != nil {
 		return nil, nil, err