diff --git a/app/vmalert/remotewrite/remotewrite.go b/app/vmalert/remotewrite/remotewrite.go
index eaac3a4bb..30d948224 100644
--- a/app/vmalert/remotewrite/remotewrite.go
+++ b/app/vmalert/remotewrite/remotewrite.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"path"
 	"strings"
 	"sync"
 	"time"
@@ -92,6 +93,10 @@ func NewClient(ctx context.Context, cfg Config) (*Client, error) {
 	if cfg.Transport == nil {
 		cfg.Transport = http.DefaultTransport.(*http.Transport).Clone()
 	}
+	cc := defaultConcurrency
+	if cfg.Concurrency > 0 {
+		cc = cfg.Concurrency
+	}
 	c := &Client{
 		c: &http.Client{
 			Timeout:   cfg.WriteTimeout,
@@ -106,10 +111,7 @@ func NewClient(ctx context.Context, cfg Config) (*Client, error) {
 		input:             make(chan prompbmarshal.TimeSeries, cfg.MaxQueueSize),
 		disablePathAppend: cfg.DisablePathAppend,
 	}
-	cc := defaultConcurrency
-	if cfg.Concurrency > 0 {
-		cc = cfg.Concurrency
-	}
+
 	for i := 0; i < cc; i++ {
 		c.run(ctx)
 	}
@@ -182,10 +184,11 @@ func (c *Client) run(ctx context.Context) {
 }
 
 var (
-	sentRows     = metrics.NewCounter(`vmalert_remotewrite_sent_rows_total`)
-	sentBytes    = metrics.NewCounter(`vmalert_remotewrite_sent_bytes_total`)
-	droppedRows  = metrics.NewCounter(`vmalert_remotewrite_dropped_rows_total`)
-	droppedBytes = metrics.NewCounter(`vmalert_remotewrite_dropped_bytes_total`)
+	sentRows            = metrics.NewCounter(`vmalert_remotewrite_sent_rows_total`)
+	sentBytes           = metrics.NewCounter(`vmalert_remotewrite_sent_bytes_total`)
+	droppedRows         = metrics.NewCounter(`vmalert_remotewrite_dropped_rows_total`)
+	droppedBytes        = metrics.NewCounter(`vmalert_remotewrite_dropped_bytes_total`)
+	bufferFlushDuration = metrics.NewHistogram(`vmalert_remotewrite_flush_duration_seconds`)
 )
 
 // flush is a blocking function that marshals WriteRequest and sends
@@ -196,6 +199,7 @@ func (c *Client) flush(ctx context.Context, wr *prompbmarshal.WriteRequest) {
 		return
 	}
 	defer prompbmarshal.ResetWriteRequest(wr)
+	defer bufferFlushDuration.UpdateDuration(time.Now())
 
 	data, err := wr.Marshal()
 	if err != nil {
@@ -237,7 +241,7 @@ func (c *Client) send(ctx context.Context, data []byte) error {
 		}
 	}
 	if !c.disablePathAppend {
-		req.URL.Path += writePath
+		req.URL.Path = path.Join(req.URL.Path, writePath)
 	}
 	resp, err := c.c.Do(req.WithContext(ctx))
 	if err != nil {