diff --git a/storage/metric/tiered/memory.go b/storage/metric/tiered/memory.go
index 9b636bb88..9341679ef 100644
--- a/storage/metric/tiered/memory.go
+++ b/storage/metric/tiered/memory.go
@@ -33,7 +33,8 @@ type stream interface {
 	add(metric.Values)
 
 	clone() metric.Values
-	expunge(age clientmodel.Timestamp) metric.Values
+	getOlderThan(age clientmodel.Timestamp) metric.Values
+	evictOlderThan(age clientmodel.Timestamp)
 
 	size() int
 	clear()
@@ -89,7 +90,19 @@ func (s *arrayStream) clone() metric.Values {
 	return clone
 }
 
-func (s *arrayStream) expunge(t clientmodel.Timestamp) metric.Values {
+func (s *arrayStream) getOlderThan(t clientmodel.Timestamp) metric.Values {
+	s.RLock()
+	defer s.RUnlock()
+
+	finder := func(i int) bool {
+		return s.values[i].Timestamp.After(t)
+	}
+
+	i := sort.Search(len(s.values), finder)
+	return s.values[:i]
+}
+
+func (s *arrayStream) evictOlderThan(t clientmodel.Timestamp) {
 	s.Lock()
 	defer s.Unlock()
 
@@ -98,10 +111,7 @@ func (s *arrayStream) expunge(t clientmodel.Timestamp) metric.Values {
 	}
 
 	i := sort.Search(len(s.values), finder)
-	expunged := s.values[:i]
 	s.values = s.values[i:]
-
-	return expunged
 }
 
 func (s *arrayStream) getValueAtTime(t clientmodel.Timestamp) metric.Values {
@@ -282,11 +292,9 @@ func (s *memorySeriesStorage) getOrCreateSeries(m clientmodel.Metric, fp *client
 }
 
 func (s *memorySeriesStorage) Flush(flushOlderThan clientmodel.Timestamp, queue chan<- clientmodel.Samples) {
-	emptySeries := []clientmodel.Fingerprint{}
-
 	s.RLock()
-	for fingerprint, stream := range s.fingerprintToSeries {
-		toArchive := stream.expunge(flushOlderThan)
+	for _, stream := range s.fingerprintToSeries {
+		toArchive := stream.getOlderThan(flushOlderThan)
 		queued := make(clientmodel.Samples, 0, len(toArchive))
 		// NOTE: This duplication will go away soon.
 		for _, value := range toArchive {
@@ -303,20 +311,29 @@ func (s *memorySeriesStorage) Flush(flushOlderThan clientmodel.Timestamp, queue
 		if len(queued) > 0 {
 			queue <- queued
 		}
+	}
+	s.RUnlock()
+}
 
+func (s *memorySeriesStorage) Evict(flushOlderThan clientmodel.Timestamp) {
+	emptySeries := []clientmodel.Fingerprint{}
+
+	s.RLock()
+	for fingerprint, stream := range s.fingerprintToSeries {
+		stream.evictOlderThan(flushOlderThan)
 		if stream.size() == 0 {
 			emptySeries = append(emptySeries, fingerprint)
 		}
 	}
 	s.RUnlock()
 
+	s.Lock()
 	for _, fingerprint := range emptySeries {
 		if series, ok := s.fingerprintToSeries[fingerprint]; ok && series.size() == 0 {
-			s.Lock()
 			s.dropSeries(&fingerprint)
-			s.Unlock()
 		}
 	}
+	s.Unlock()
 }
 
 // Drop a label value from the label names to label values index.
diff --git a/storage/metric/tiered/memory_test.go b/storage/metric/tiered/memory_test.go
index b3b52c8fe..a6a53bb02 100644
--- a/storage/metric/tiered/memory_test.go
+++ b/storage/metric/tiered/memory_test.go
@@ -171,7 +171,8 @@ func TestDroppedSeriesIndexRegression(t *testing.T) {
 	}
 
 	toDisk := make(chan clientmodel.Samples, 2)
-	s.Flush(clientmodel.TimestampFromTime(time.Date(2001, 0, 0, 0, 0, 0, 0, time.UTC)), toDisk)
+	flushOlderThan := clientmodel.TimestampFromTime(time.Date(2001, 0, 0, 0, 0, 0, 0, time.UTC))
+	s.Flush(flushOlderThan, toDisk)
 	if len(toDisk) != 1 {
 		t.Fatalf("Got %d disk sample lists, expected 1", len(toDisk))
 	}
@@ -179,6 +180,7 @@ func TestDroppedSeriesIndexRegression(t *testing.T) {
 	if len(diskSamples) != 1 {
 		t.Fatalf("Got %d disk samples, expected 1", len(diskSamples))
 	}
+	s.Evict(flushOlderThan)
 
 	fps, err = s.GetFingerprintsForLabelMatchers(labelMatchersFromLabelSet(common))
 	if err != nil {
diff --git a/storage/metric/tiered/tiered.go b/storage/metric/tiered/tiered.go
index e0bd6031c..cc02e8480 100644
--- a/storage/metric/tiered/tiered.go
+++ b/storage/metric/tiered/tiered.go
@@ -364,6 +364,7 @@ func (t *TieredStorage) flushMemory(ttl time.Duration) {
 		glog.Infof("Writing %d samples...", len(samples))
 		t.DiskStorage.AppendSamples(samples)
 	}
+	t.memoryArena.Evict(flushOlderThan)
 
 	glog.Info("Done flushing.")
 }
diff --git a/web/api/api.go b/web/api/api.go
index 3d749380b..4c42ba6ec 100644
--- a/web/api/api.go
+++ b/web/api/api.go
@@ -15,6 +15,7 @@ package api
 
 import (
 	"net/http"
+
 	"github.com/prometheus/client_golang/prometheus"
 
 	"github.com/prometheus/prometheus/config"