diff --git a/report/metrics.go b/report/metrics.go
index 1d8fe50ad..2e0458c11 100644
--- a/report/metrics.go
+++ b/report/metrics.go
@@ -52,12 +52,8 @@ type Metric struct {
 	Min, Max float64
 }
 
-// Following two functions are exported for testing only: make sure there are samples before calling.
-// First gives the timestamp of the first sample
-func (m Metric) First() time.Time { return m.Samples[0].Timestamp }
-
-// Last gives the timestamp of the last sample
-func (m Metric) Last() time.Time { return m.Samples[len(m.Samples)-1].Timestamp }
+func (m Metric) first() time.Time { return m.Samples[0].Timestamp }
+func (m Metric) last() time.Time  { return m.Samples[len(m.Samples)-1].Timestamp }
 
 // Sample is a single datapoint of a metric.
 type Sample struct {
@@ -127,7 +123,7 @@ func (m Metric) Merge(other Metric) Metric {
 		return other
 	case len(other.Samples) == 0:
 		return m
-	case other.First().After(m.Last()):
+	case other.first().After(m.last()):
 		samplesOut := make([]Sample, len(m.Samples)+len(other.Samples))
 		copy(samplesOut, m.Samples)
 		copy(samplesOut[len(m.Samples):], other.Samples)
@@ -136,7 +132,7 @@ func (m Metric) Merge(other Metric) Metric {
 			Max:     math.Max(m.Max, other.Max),
 			Min:     math.Min(m.Min, other.Min),
 		}
-	case m.First().After(other.Last()):
+	case m.first().After(other.last()):
 		samplesOut := make([]Sample, len(m.Samples)+len(other.Samples))
 		copy(samplesOut, other.Samples)
 		copy(samplesOut[len(other.Samples):], m.Samples)
diff --git a/report/metrics_test.go b/report/metrics_test.go
index 08ffc40ac..1eaa6bafc 100644
--- a/report/metrics_test.go
+++ b/report/metrics_test.go
@@ -49,13 +49,7 @@ func TestMetricsCopy(t *testing.T) {
 	}
 }
 
-func checkMetric(t *testing.T, metric report.Metric, first, last time.Time, min, max float64) {
-	if !metric.First().Equal(first) {
-		t.Errorf("Expected metric.First == %q, but was: %q", first, metric.First())
-	}
-	if !metric.Last().Equal(last) {
-		t.Errorf("Expected metric.Last == %q, but was: %q", last, metric.Last())
-	}
+func checkMetric(t *testing.T, metric report.Metric, min, max float64) {
 	if metric.Min != min {
 		t.Errorf("Expected metric.Min == %f, but was: %f", min, metric.Min)
 	}
@@ -70,16 +64,16 @@ func TestMetricFirstLastMinMax(t *testing.T) {
 
 	metric1 := report.MakeMetric([]report.Sample{{Timestamp: t1, Value: -0.1}, {Timestamp: t2, Value: 0.2}})
 
-	checkMetric(t, metric1, t1, t2, -0.1, 0.2)
-	checkMetric(t, metric1.Merge(metric1), t1, t2, -0.1, 0.2)
+	checkMetric(t, metric1, -0.1, 0.2)
+	checkMetric(t, metric1.Merge(metric1), -0.1, 0.2)
 
 	t3 := time.Now().Add(2 * time.Minute)
 	t4 := time.Now().Add(3 * time.Minute)
 	metric2 := report.MakeMetric([]report.Sample{{Timestamp: t3, Value: 0.31}, {Timestamp: t4, Value: 0.4}})
 
-	checkMetric(t, metric2, t3, t4, 0.31, 0.4)
-	checkMetric(t, metric1.Merge(metric2), t1, t4, -0.1, 0.4)
-	checkMetric(t, metric2.Merge(metric1), t1, t4, -0.1, 0.4)
+	checkMetric(t, metric2, 0.31, 0.4)
+	checkMetric(t, metric1.Merge(metric2), -0.1, 0.4)
+	checkMetric(t, metric2.Merge(metric1), -0.1, 0.4)
 }
 
 func TestMetricMerge(t *testing.T) {
@@ -98,14 +92,6 @@ func TestMetricMerge(t *testing.T) {
 	if !reflect.DeepEqual(want, have) {
 		t.Errorf("diff: %s", test.Diff(want, have))
 	}
-
-	// Check it didn't modify metric1
-	checkMetric(t, metric1, t2, t3, 0.2, 0.31)
-
-	// Check the result is not the same instance as metric1
-	if &metric1 == &have {
-		t.Errorf("Expected different pointers for metric1 and have, but both were: %p", &have)
-	}
 }
 
 func TestMetricMarshalling(t *testing.T) {