diff --git a/pkg/metrics/metrics.go b/pkg/metrics/metrics.go
index 4e7749d07..8927e3245 100644
--- a/pkg/metrics/metrics.go
+++ b/pkg/metrics/metrics.go
@@ -191,36 +191,29 @@ func (r *standardRegistry) ServiceServerUpGauge() metrics.Gauge {
 // used when producing observations without explicitly setting the observed value.
 type ScalableHistogram interface {
 	With(labelValues ...string) ScalableHistogram
-	StartAt(t time.Time)
 	Observe(v float64)
-	ObserveDuration()
+	ObserveFromStart(start time.Time)
 }
 
 // HistogramWithScale is a histogram that will convert its observed value to the specified unit.
 type HistogramWithScale struct {
 	histogram metrics.Histogram
 	unit      time.Duration
-	start     time.Time
 }
 
 // With implements ScalableHistogram.
 func (s *HistogramWithScale) With(labelValues ...string) ScalableHistogram {
-	s.histogram = s.histogram.With(labelValues...)
-	return s
+	h, _ := NewHistogramWithScale(s.histogram.With(labelValues...), s.unit)
+	return h
 }
 
-// StartAt implements ScalableHistogram.
-func (s *HistogramWithScale) StartAt(t time.Time) {
-	s.start = t
-}
-
-// ObserveDuration implements ScalableHistogram.
-func (s *HistogramWithScale) ObserveDuration() {
+// ObserveFromStart implements ScalableHistogram.
+func (s *HistogramWithScale) ObserveFromStart(start time.Time) {
 	if s.unit <= 0 {
 		return
 	}
 
-	d := float64(time.Since(s.start).Nanoseconds()) / float64(s.unit)
+	d := float64(time.Since(start).Nanoseconds()) / float64(s.unit)
 	if d < 0 {
 		d = 0
 	}
@@ -251,17 +244,10 @@ func NewMultiHistogram(h ...ScalableHistogram) MultiHistogram {
 	return MultiHistogram(h)
 }
 
-// StartAt implements ScalableHistogram.
-func (h MultiHistogram) StartAt(t time.Time) {
+// ObserveFromStart implements ScalableHistogram.
+func (h MultiHistogram) ObserveFromStart(start time.Time) {
 	for _, histogram := range h {
-		histogram.StartAt(t)
-	}
-}
-
-// ObserveDuration implements ScalableHistogram.
-func (h MultiHistogram) ObserveDuration() {
-	for _, histogram := range h {
-		histogram.ObserveDuration()
+		histogram.ObserveFromStart(start)
 	}
 }
 
diff --git a/pkg/metrics/metrics_test.go b/pkg/metrics/metrics_test.go
index 221193a42..522be234f 100644
--- a/pkg/metrics/metrics_test.go
+++ b/pkg/metrics/metrics_test.go
@@ -19,9 +19,9 @@ func TestScalableHistogram(t *testing.T) {
 
 	ticker := time.NewTicker(500 * time.Millisecond)
 	<-ticker.C
-	sh.StartAt(time.Now())
+	start := time.Now()
 	<-ticker.C
-	sh.ObserveDuration()
+	sh.ObserveFromStart(start)
 
 	var b bytes.Buffer
 	h.Print(&b)
@@ -99,9 +99,7 @@ func (c *histogramMock) With(labelValues ...string) ScalableHistogram {
 
 func (c *histogramMock) Start() {}
 
-func (c *histogramMock) StartAt(t time.Time) {}
-
-func (c *histogramMock) ObserveDuration() {}
+func (c *histogramMock) ObserveFromStart(t time.Time) {}
 
 func (c *histogramMock) Observe(v float64) {
 	c.lastHistogramValue = v
diff --git a/pkg/middlewares/metrics/metrics.go b/pkg/middlewares/metrics/metrics.go
index 53ce890fa..1e55467b6 100644
--- a/pkg/middlewares/metrics/metrics.go
+++ b/pkg/middlewares/metrics/metrics.go
@@ -96,11 +96,9 @@ func (m *metricsMiddleware) ServeHTTP(rw http.ResponseWriter, req *http.Request)
 	labels = append(labels, "code", strconv.Itoa(recorder.getCode()))
 
 	histograms := m.reqDurationHistogram.With(labels...)
-	histograms.StartAt(start)
+	histograms.ObserveFromStart(start)
 
 	m.reqsCounter.With(labels...).Add(1)
-
-	histograms.ObserveDuration()
 }
 
 func getRequestProtocol(req *http.Request) string {