diff --git a/promql/functions.go b/promql/functions.go
index 0d3ec41951..433c06f023 100644
--- a/promql/functions.go
+++ b/promql/functions.go
@@ -548,7 +548,7 @@ func linearRegression(samples []model.SamplePair, interceptTime model.Time) (slo
 
 	slope = covXY / varX
 	intercept = sumY/n - slope*sumX/n
-	return
+	return slope, intercept
 }
 
 // === deriv(node model.ValMatrix) Vector ===
diff --git a/storage/local/preload.go b/storage/local/preload.go
index b0113bd6be..fb6a21f64b 100644
--- a/storage/local/preload.go
+++ b/storage/local/preload.go
@@ -30,7 +30,7 @@ func (p *memorySeriesPreloader) PreloadRange(
 	fp model.Fingerprint,
 	from model.Time, through model.Time,
 ) SeriesIterator {
-	cds, iter := p.storage.preloadChunksForRange(fp, from, through, false)
+	cds, iter := p.storage.preloadChunksForRange(fp, from, through)
 	p.pinnedChunkDescs = append(p.pinnedChunkDescs, cds...)
 	return iter
 }
@@ -40,7 +40,7 @@ func (p *memorySeriesPreloader) PreloadInstant(
 	fp model.Fingerprint,
 	timestamp model.Time, stalenessDelta time.Duration,
 ) SeriesIterator {
-	cds, iter := p.storage.preloadChunksForRange(fp, timestamp.Add(-stalenessDelta), timestamp, true)
+	cds, iter := p.storage.preloadChunksForInstant(fp, timestamp.Add(-stalenessDelta), timestamp)
 	p.pinnedChunkDescs = append(p.pinnedChunkDescs, cds...)
 	return iter
 }
diff --git a/storage/local/series.go b/storage/local/series.go
index f76d5ee27b..51ad865a93 100644
--- a/storage/local/series.go
+++ b/storage/local/series.go
@@ -399,30 +399,40 @@ func (s *memorySeries) newIterator(pinnedChunkDescs []*chunkDesc, quarantine fun
 	}
 }
 
+// preloadChunksForInstant preloads chunks for the latest value in the given
+// range. If the last sample saved in the memorySeries itself is the latest
+// value in the given range, it will in fact preload zero chunks and just take
+// that value.
+func (s *memorySeries) preloadChunksForInstant(
+	fp model.Fingerprint,
+	from model.Time, through model.Time,
+	mss *memorySeriesStorage,
+) ([]*chunkDesc, SeriesIterator, error) {
+	// If we have a lastSamplePair in the series, and thas last samplePair
+	// is in the interval, just take it in a singleSampleSeriesIterator. No
+	// need to pin or load anything.
+	lastSample := s.lastSamplePair()
+	if !through.Before(lastSample.Timestamp) &&
+		!from.After(lastSample.Timestamp) &&
+		lastSample != ZeroSamplePair {
+		iter := &boundedIterator{
+			it:    &singleSampleSeriesIterator{samplePair: lastSample},
+			start: model.Now().Add(-mss.dropAfter),
+		}
+		return nil, iter, nil
+	}
+	// If we are here, we are out of luck and have to delegate to the more
+	// expensive method.
+	return s.preloadChunksForRange(fp, from, through, mss)
+}
+
 // preloadChunksForRange loads chunks for the given range from the persistence.
 // The caller must have locked the fingerprint of the series.
 func (s *memorySeries) preloadChunksForRange(
 	fp model.Fingerprint,
 	from model.Time, through model.Time,
-	lastSampleOnly bool,
 	mss *memorySeriesStorage,
 ) ([]*chunkDesc, SeriesIterator, error) {
-	// If we have to preload for only one sample, and we have a
-	// lastSamplePair in the series, and thas last samplePair is in the
-	// interval, just take it in a singleSampleSeriesIterator. No need to
-	// pin or load anything.
-	if lastSampleOnly {
-		lastSample := s.lastSamplePair()
-		if !through.Before(lastSample.Timestamp) &&
-			!from.After(lastSample.Timestamp) &&
-			lastSample != ZeroSamplePair {
-			iter := &boundedIterator{
-				it:    &singleSampleSeriesIterator{samplePair: lastSample},
-				start: model.Now().Add(-mss.dropAfter),
-			}
-			return nil, iter, nil
-		}
-	}
 	firstChunkDescTime := model.Latest
 	if len(s.chunkDescs) > 0 {
 		firstChunkDescTime = s.chunkDescs[0].firstTime()
diff --git a/storage/local/storage.go b/storage/local/storage.go
index 2d99c073f3..ede1bfc612 100644
--- a/storage/local/storage.go
+++ b/storage/local/storage.go
@@ -695,46 +695,76 @@ func (s *memorySeriesStorage) getOrCreateSeries(fp model.Fingerprint, m model.Me
 	return series, nil
 }
 
+// getSeriesForRange is a helper method for preloadChunksForRange and preloadChunksForInstant.
+func (s *memorySeriesStorage) getSeriesForRange(
+	fp model.Fingerprint,
+	from model.Time, through model.Time,
+) *memorySeries {
+	series, ok := s.fpToSeries.get(fp)
+	if ok {
+		return series
+	}
+	has, first, last, err := s.persistence.hasArchivedMetric(fp)
+	if err != nil {
+		log.With("fingerprint", fp).With("error", err).Error("Archive index error while preloading chunks.")
+		return nil
+	}
+	if !has {
+		s.invalidPreloadRequestsCount.Inc()
+		return nil
+	}
+	if last.Before(from) || first.After(through) {
+		return nil
+	}
+	metric, err := s.persistence.archivedMetric(fp)
+	if err != nil {
+		log.With("fingerprint", fp).With("error", err).Error("Archive index error while preloading chunks.")
+		return nil
+	}
+	series, err = s.getOrCreateSeries(fp, metric)
+	if err != nil {
+		// getOrCreateSeries took care of quarantining already.
+		return nil
+	}
+	return series
+}
+
 func (s *memorySeriesStorage) preloadChunksForRange(
 	fp model.Fingerprint,
 	from model.Time, through model.Time,
-	lastSampleOnly bool,
 ) ([]*chunkDesc, SeriesIterator) {
 	s.fpLocker.Lock(fp)
 	defer s.fpLocker.Unlock(fp)
 
-	series, ok := s.fpToSeries.get(fp)
-	if !ok {
-		has, first, last, err := s.persistence.hasArchivedMetric(fp)
-		if err != nil {
-			log.With("fingerprint", fp).With("error", err).Error("Archive index error while preloading chunks.")
-			return nil, nopIter
-		}
-		if !has {
-			s.invalidPreloadRequestsCount.Inc()
-			return nil, nopIter
-		}
-		if from.Before(last) && through.After(first) {
-			metric, err := s.persistence.archivedMetric(fp)
-			if err != nil {
-				log.With("fingerprint", fp).With("error", err).Error("Archive index error while preloading chunks.")
-				return nil, nopIter
-			}
-			series, err = s.getOrCreateSeries(fp, metric)
-			if err != nil {
-				log.With("fingerprint", fp).With("error", err).Error("Error while retrieving series.")
-				return nil, nopIter
-			}
-		} else {
-			return nil, nopIter
-		}
+	series := s.getSeriesForRange(fp, from, through)
+	if series == nil {
+		return nil, nopIter
 	}
-	cds, it, err := series.preloadChunksForRange(fp, from, through, lastSampleOnly, s)
+	cds, iter, err := series.preloadChunksForRange(fp, from, through, s)
 	if err != nil {
 		s.quarantineSeries(fp, series.metric, err)
 		return nil, nopIter
 	}
-	return cds, it
+	return cds, iter
+}
+
+func (s *memorySeriesStorage) preloadChunksForInstant(
+	fp model.Fingerprint,
+	from model.Time, through model.Time,
+) ([]*chunkDesc, SeriesIterator) {
+	s.fpLocker.Lock(fp)
+	defer s.fpLocker.Unlock(fp)
+
+	series := s.getSeriesForRange(fp, from, through)
+	if series == nil {
+		return nil, nopIter
+	}
+	cds, iter, err := series.preloadChunksForInstant(fp, from, through, s)
+	if err != nil {
+		s.quarantineSeries(fp, series.metric, err)
+		return nil, nopIter
+	}
+	return cds, iter
 }
 
 func (s *memorySeriesStorage) handleEvictList() {
diff --git a/storage/local/storage_test.go b/storage/local/storage_test.go
index 97fa450ba7..33d1a99183 100644
--- a/storage/local/storage_test.go
+++ b/storage/local/storage_test.go
@@ -489,12 +489,12 @@ func TestDropMetrics(t *testing.T) {
 		t.Errorf("unexpected number of fingerprints: %d", len(fps2))
 	}
 
-	_, it := s.preloadChunksForRange(fpList[0], model.Earliest, model.Latest, false)
+	_, it := s.preloadChunksForRange(fpList[0], model.Earliest, model.Latest)
 	if vals := it.RangeValues(metric.Interval{OldestInclusive: insertStart, NewestInclusive: now}); len(vals) != 0 {
 		t.Errorf("unexpected number of samples: %d", len(vals))
 	}
 
-	_, it = s.preloadChunksForRange(fpList[1], model.Earliest, model.Latest, false)
+	_, it = s.preloadChunksForRange(fpList[1], model.Earliest, model.Latest)
 	if vals := it.RangeValues(metric.Interval{OldestInclusive: insertStart, NewestInclusive: now}); len(vals) != N {
 		t.Errorf("unexpected number of samples: %d", len(vals))
 	}
@@ -516,12 +516,12 @@ func TestDropMetrics(t *testing.T) {
 		t.Errorf("unexpected number of fingerprints: %d", len(fps3))
 	}
 
-	_, it = s.preloadChunksForRange(fpList[0], model.Earliest, model.Latest, false)
+	_, it = s.preloadChunksForRange(fpList[0], model.Earliest, model.Latest)
 	if vals := it.RangeValues(metric.Interval{OldestInclusive: insertStart, NewestInclusive: now}); len(vals) != 0 {
 		t.Errorf("unexpected number of samples: %d", len(vals))
 	}
 
-	_, it = s.preloadChunksForRange(fpList[1], model.Earliest, model.Latest, false)
+	_, it = s.preloadChunksForRange(fpList[1], model.Earliest, model.Latest)
 	if vals := it.RangeValues(metric.Interval{OldestInclusive: insertStart, NewestInclusive: now}); len(vals) != 0 {
 		t.Errorf("unexpected number of samples: %d", len(vals))
 	}
@@ -739,7 +739,7 @@ func testValueAtOrBeforeTime(t *testing.T, encoding chunkEncoding) {
 
 	fp := model.Metric{}.FastFingerprint()
 
-	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest, false)
+	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest)
 
 	// #1 Exactly on a sample.
 	for i, expected := range samples {
@@ -813,7 +813,7 @@ func benchmarkValueAtOrBeforeTime(b *testing.B, encoding chunkEncoding) {
 
 	fp := model.Metric{}.FastFingerprint()
 
-	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest, false)
+	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest)
 
 	b.ResetTimer()
 
@@ -891,7 +891,7 @@ func testRangeValues(t *testing.T, encoding chunkEncoding) {
 
 	fp := model.Metric{}.FastFingerprint()
 
-	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest, false)
+	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest)
 
 	// #1 Zero length interval at sample.
 	for i, expected := range samples {
@@ -1043,7 +1043,7 @@ func benchmarkRangeValues(b *testing.B, encoding chunkEncoding) {
 
 	fp := model.Metric{}.FastFingerprint()
 
-	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest, false)
+	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest)
 
 	b.ResetTimer()
 
@@ -1089,7 +1089,7 @@ func testEvictAndPurgeSeries(t *testing.T, encoding chunkEncoding) {
 
 	// Drop ~half of the chunks.
 	s.maintainMemorySeries(fp, 10000)
-	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest, false)
+	_, it := s.preloadChunksForRange(fp, model.Earliest, model.Latest)
 	actual := it.RangeValues(metric.Interval{
 		OldestInclusive: 0,
 		NewestInclusive: 100000,
@@ -1107,7 +1107,7 @@ func testEvictAndPurgeSeries(t *testing.T, encoding chunkEncoding) {
 
 	// Drop everything.
 	s.maintainMemorySeries(fp, 100000)
-	_, it = s.preloadChunksForRange(fp, model.Earliest, model.Latest, false)
+	_, it = s.preloadChunksForRange(fp, model.Earliest, model.Latest)
 	actual = it.RangeValues(metric.Interval{
 		OldestInclusive: 0,
 		NewestInclusive: 100000,