diff --git a/storage/local/chunk.go b/storage/local/chunk.go
index d8b1ae2b8d..582789fb7e 100644
--- a/storage/local/chunk.go
+++ b/storage/local/chunk.go
@@ -259,18 +259,13 @@ type chunk interface {
 
 // A chunkIterator enables efficient access to the content of a chunk. It is
 // generally not safe to use a chunkIterator concurrently with or after chunk
-// mutation.
+// mutation. The error returned by any of the methods is always the last error
+// encountered by the iterator, i.e. once an error has been encountered, no
+// method will ever return a nil error again. In general, errors signal data
+// corruption in the chunk and require quarantining.
 type chunkIterator interface {
-	// length returns the number of samples in the chunk.
-	length() int
-	// Gets the timestamp of the n-th sample in the chunk.
-	timestampAtIndex(int) (model.Time, error)
 	// Gets the last timestamp in the chunk.
 	lastTimestamp() (model.Time, error)
-	// Gets the sample value of the n-th sample in the chunk.
-	sampleValueAtIndex(int) (model.SampleValue, error)
-	// Gets the last sample value in the chunk.
-	lastSampleValue() (model.SampleValue, error)
 	// Gets the value that is closest before the given time. In case a value
 	// exists at precisely the given time, that value is returned. If no
 	// applicable value exists, ZeroSamplePair is returned.
@@ -280,35 +275,48 @@ type chunkIterator interface {
 	// Whether a given timestamp is contained between first and last value
 	// in the chunk.
 	contains(model.Time) (bool, error)
-	// values returns a channel, from which all sample values in the chunk
-	// can be received in order. The channel is closed after the last
-	// one. It is generally not safe to mutate the chunk while the channel
-	// is still open. If a value is returned with error!=nil, no further
-	// values will be returned and the channel is closed.
-	values() <-chan struct {
-		model.SamplePair
-		error
-	}
+	// scan, value, and err implement a bufio.Scanner-like interface.  The
+	// scan method advances the iterator to the next value in the chunk and
+	// returns true if that worked. In that case, the value method will
+	// return the sample pair the iterator has advanced to. If the scan
+	// method returns false, either an error has occured or the end of the
+	// chunk has been reached. In the former case, the err method will
+	// return the error. In the latter case, the err method will return nil.
+	// Upon creation, the iterator is at position "minus one". After the
+	// first scan call, value will return the 1st value in the
+	// chunk. valueAtOrBeforeTime and rangeValues all modify the iterator
+	// position, too. They behave as if their return values were retrieved
+	// after a scan call, i.e. calling the value or err methods after a call
+	// to those methods will retrieve the same return value again (or the
+	// last value in the range in case of rangeValues), and subsequent scan
+	// calls will advance the iterator from there.
+	scan() bool
+	value() model.SamplePair
+	err() error
 }
 
 func transcodeAndAdd(dst chunk, src chunk, s model.SamplePair) ([]chunk, error) {
 	chunkOps.WithLabelValues(transcode).Inc()
 
-	head := dst
-	body := []chunk{}
-	for v := range src.newIterator().values() {
-		if v.error != nil {
-			return nil, v.error
-		}
-		newChunks, err := head.add(v.SamplePair)
-		if err != nil {
+	var (
+		head            = dst
+		body, newChunks []chunk
+		err             error
+	)
+
+	it := src.newIterator()
+	for it.scan() {
+		if newChunks, err = head.add(it.value()); err != nil {
 			return nil, err
 		}
 		body = append(body, newChunks[:len(newChunks)-1]...)
 		head = newChunks[len(newChunks)-1]
 	}
-	newChunks, err := head.add(s)
-	if err != nil {
+	if it.err() != nil {
+		return nil, it.err()
+	}
+
+	if newChunks, err = head.add(s); err != nil {
 		return nil, err
 	}
 	return append(body, newChunks...), nil
diff --git a/storage/local/delta.go b/storage/local/delta.go
index c787020722..3dd41cf775 100644
--- a/storage/local/delta.go
+++ b/storage/local/delta.go
@@ -202,13 +202,15 @@ func (c deltaEncodedChunk) firstTime() model.Time {
 // newIterator implements chunk.
 func (c *deltaEncodedChunk) newIterator() chunkIterator {
 	return &deltaEncodedChunkIterator{
-		c:      *c,
-		len:    c.len(),
-		baseT:  c.baseTime(),
-		baseV:  c.baseValue(),
-		tBytes: c.timeBytes(),
-		vBytes: c.valueBytes(),
-		isInt:  c.isInt(),
+		c:         *c,
+		len:       c.len(),
+		baseT:     c.baseTime(),
+		baseV:     c.baseValue(),
+		tBytes:    c.timeBytes(),
+		vBytes:    c.valueBytes(),
+		isInt:     c.isInt(),
+		pos:       -1,
+		lastValue: ZeroSamplePair,
 	}
 }
 
@@ -311,176 +313,130 @@ type deltaEncodedChunkIterator struct {
 	baseV          model.SampleValue
 	tBytes, vBytes deltaBytes
 	isInt          bool
-}
-
-// length implements chunkIterator.
-func (it *deltaEncodedChunkIterator) length() int { return it.len }
-
-// valueAtOrBeforeTime implements chunkIterator.
-func (it *deltaEncodedChunkIterator) valueAtOrBeforeTime(t model.Time) (model.SamplePair, error) {
-	var lastErr error
-	i := sort.Search(it.len, func(i int) bool {
-		ts, err := it.timestampAtIndex(i)
-		if err != nil {
-			lastErr = err
-		}
-		return ts.After(t)
-	})
-	if i == 0 || lastErr != nil {
-		return ZeroSamplePair, lastErr
-	}
-	ts, err := it.timestampAtIndex(i - 1)
-	if err != nil {
-		return ZeroSamplePair, err
-	}
-	v, err := it.sampleValueAtIndex(i - 1)
-	if err != nil {
-		return ZeroSamplePair, err
-	}
-	return model.SamplePair{Timestamp: ts, Value: v}, nil
-}
-
-// rangeValues implements chunkIterator.
-func (it *deltaEncodedChunkIterator) rangeValues(in metric.Interval) ([]model.SamplePair, error) {
-	var lastErr error
-
-	oldest := sort.Search(it.len, func(i int) bool {
-		t, err := it.timestampAtIndex(i)
-		if err != nil {
-			lastErr = err
-		}
-		return !t.Before(in.OldestInclusive)
-	})
-
-	newest := sort.Search(it.len, func(i int) bool {
-		t, err := it.timestampAtIndex(i)
-		if err != nil {
-			lastErr = err
-		}
-		return t.After(in.NewestInclusive)
-	})
-
-	if oldest == it.len || lastErr != nil {
-		return nil, lastErr
-	}
-
-	result := make([]model.SamplePair, 0, newest-oldest)
-	for i := oldest; i < newest; i++ {
-		t, err := it.timestampAtIndex(i)
-		if err != nil {
-			return nil, err
-		}
-		v, err := it.sampleValueAtIndex(i)
-		if err != nil {
-			return nil, err
-		}
-		result = append(result, model.SamplePair{Timestamp: t, Value: v})
-	}
-	return result, nil
-}
-
-// contains implements chunkIterator.
-func (it *deltaEncodedChunkIterator) contains(t model.Time) (bool, error) {
-	lastT, err := it.timestampAtIndex(it.len - 1)
-	if err != nil {
-		return false, err
-	}
-	return !t.Before(it.baseT) && !t.After(lastT), nil
-}
-
-// values implements chunkIterator.
-func (it *deltaEncodedChunkIterator) values() <-chan struct {
-	model.SamplePair
-	error
-} {
-	valuesChan := make(chan struct {
-		model.SamplePair
-		error
-	})
-	go func() {
-		for i := 0; i < it.len; i++ {
-			t, err := it.timestampAtIndex(i)
-			if err != nil {
-				valuesChan <- struct {
-					model.SamplePair
-					error
-				}{ZeroSamplePair, err}
-				break
-			}
-			v, err := it.sampleValueAtIndex(i)
-			if err != nil {
-				valuesChan <- struct {
-					model.SamplePair
-					error
-				}{ZeroSamplePair, err}
-				break
-			}
-			valuesChan <- struct {
-				model.SamplePair
-				error
-			}{model.SamplePair{Timestamp: t, Value: v}, nil}
-		}
-		close(valuesChan)
-	}()
-	return valuesChan
-}
-
-// timestampAtIndex implements chunkIterator.
-func (it *deltaEncodedChunkIterator) timestampAtIndex(idx int) (model.Time, error) {
-	offset := deltaHeaderBytes + idx*int(it.tBytes+it.vBytes)
-
-	switch it.tBytes {
-	case d1:
-		return it.baseT + model.Time(uint8(it.c[offset])), nil
-	case d2:
-		return it.baseT + model.Time(binary.LittleEndian.Uint16(it.c[offset:])), nil
-	case d4:
-		return it.baseT + model.Time(binary.LittleEndian.Uint32(it.c[offset:])), nil
-	case d8:
-		// Take absolute value for d8.
-		return model.Time(binary.LittleEndian.Uint64(it.c[offset:])), nil
-	default:
-		return 0, fmt.Errorf("invalid number of bytes for time delta: %d", it.tBytes)
-	}
+	pos            int
+	lastValue      model.SamplePair
+	lastErr        error
 }
 
 // lastTimestamp implements chunkIterator.
 func (it *deltaEncodedChunkIterator) lastTimestamp() (model.Time, error) {
-	return it.timestampAtIndex(it.len - 1)
+	return it.timestampAtIndex(it.len - 1), it.lastErr
 }
 
-// sampleValueAtIndex implements chunkIterator.
-func (it *deltaEncodedChunkIterator) sampleValueAtIndex(idx int) (model.SampleValue, error) {
+// valueAtOrBeforeTime implements chunkIterator.
+func (it *deltaEncodedChunkIterator) valueAtOrBeforeTime(t model.Time) (model.SamplePair, error) {
+	i := sort.Search(it.len, func(i int) bool {
+		return it.timestampAtIndex(i).After(t)
+	})
+	if i == 0 || it.lastErr != nil {
+		return ZeroSamplePair, it.lastErr
+	}
+	it.pos = i - 1
+	it.lastValue = model.SamplePair{
+		Timestamp: it.timestampAtIndex(i - 1),
+		Value:     it.sampleValueAtIndex(i - 1),
+	}
+	return it.lastValue, it.lastErr
+}
+
+// rangeValues implements chunkIterator.
+func (it *deltaEncodedChunkIterator) rangeValues(in metric.Interval) ([]model.SamplePair, error) {
+	oldest := sort.Search(it.len, func(i int) bool {
+		return !it.timestampAtIndex(i).Before(in.OldestInclusive)
+	})
+	newest := sort.Search(it.len, func(i int) bool {
+		return it.timestampAtIndex(i).After(in.NewestInclusive)
+	})
+	if oldest == it.len || it.lastErr != nil {
+		return nil, it.lastErr
+	}
+
+	result := make([]model.SamplePair, 0, newest-oldest)
+	for i := oldest; i < newest; i++ {
+		it.pos = i
+		it.lastValue = model.SamplePair{
+			Timestamp: it.timestampAtIndex(i),
+			Value:     it.sampleValueAtIndex(i),
+		}
+		result = append(result, it.lastValue)
+	}
+	return result, it.lastErr
+}
+
+// contains implements chunkIterator.
+func (it *deltaEncodedChunkIterator) contains(t model.Time) (bool, error) {
+	return !t.Before(it.baseT) && !t.After(it.timestampAtIndex(it.len-1)), it.lastErr
+}
+
+// scan implements chunkIterator.
+func (it *deltaEncodedChunkIterator) scan() bool {
+	it.pos++
+	if it.pos >= it.len {
+		return false
+	}
+	it.lastValue = model.SamplePair{
+		Timestamp: it.timestampAtIndex(it.pos),
+		Value:     it.sampleValueAtIndex(it.pos),
+	}
+	return it.lastErr == nil
+}
+
+// value implements chunkIterator.
+func (it *deltaEncodedChunkIterator) value() model.SamplePair {
+	return it.lastValue
+}
+
+// err implements chunkIterator.
+func (it *deltaEncodedChunkIterator) err() error {
+	return it.lastErr
+}
+
+func (it *deltaEncodedChunkIterator) timestampAtIndex(idx int) model.Time {
+	offset := deltaHeaderBytes + idx*int(it.tBytes+it.vBytes)
+
+	switch it.tBytes {
+	case d1:
+		return it.baseT + model.Time(uint8(it.c[offset]))
+	case d2:
+		return it.baseT + model.Time(binary.LittleEndian.Uint16(it.c[offset:]))
+	case d4:
+		return it.baseT + model.Time(binary.LittleEndian.Uint32(it.c[offset:]))
+	case d8:
+		// Take absolute value for d8.
+		return model.Time(binary.LittleEndian.Uint64(it.c[offset:]))
+	default:
+		it.lastErr = fmt.Errorf("invalid number of bytes for time delta: %d", it.tBytes)
+	}
+	return model.Earliest
+}
+
+func (it *deltaEncodedChunkIterator) sampleValueAtIndex(idx int) model.SampleValue {
 	offset := deltaHeaderBytes + idx*int(it.tBytes+it.vBytes) + int(it.tBytes)
 
 	if it.isInt {
 		switch it.vBytes {
 		case d0:
-			return it.baseV, nil
+			return it.baseV
 		case d1:
-			return it.baseV + model.SampleValue(int8(it.c[offset])), nil
+			return it.baseV + model.SampleValue(int8(it.c[offset]))
 		case d2:
-			return it.baseV + model.SampleValue(int16(binary.LittleEndian.Uint16(it.c[offset:]))), nil
+			return it.baseV + model.SampleValue(int16(binary.LittleEndian.Uint16(it.c[offset:])))
 		case d4:
-			return it.baseV + model.SampleValue(int32(binary.LittleEndian.Uint32(it.c[offset:]))), nil
+			return it.baseV + model.SampleValue(int32(binary.LittleEndian.Uint32(it.c[offset:])))
 		// No d8 for ints.
 		default:
-			return 0, fmt.Errorf("invalid number of bytes for integer delta: %d", it.vBytes)
+			it.lastErr = fmt.Errorf("invalid number of bytes for integer delta: %d", it.vBytes)
 		}
 	} else {
 		switch it.vBytes {
 		case d4:
-			return it.baseV + model.SampleValue(math.Float32frombits(binary.LittleEndian.Uint32(it.c[offset:]))), nil
+			return it.baseV + model.SampleValue(math.Float32frombits(binary.LittleEndian.Uint32(it.c[offset:])))
 		case d8:
 			// Take absolute value for d8.
-			return model.SampleValue(math.Float64frombits(binary.LittleEndian.Uint64(it.c[offset:]))), nil
+			return model.SampleValue(math.Float64frombits(binary.LittleEndian.Uint64(it.c[offset:])))
 		default:
-			return 0, fmt.Errorf("invalid number of bytes for floating point delta: %d", it.vBytes)
+			it.lastErr = fmt.Errorf("invalid number of bytes for floating point delta: %d", it.vBytes)
 		}
 	}
-}
-
-// lastSampleValue implements chunkIterator.
-func (it *deltaEncodedChunkIterator) lastSampleValue() (model.SampleValue, error) {
-	return it.sampleValueAtIndex(it.len - 1)
+	return 0
 }
diff --git a/storage/local/doubledelta.go b/storage/local/doubledelta.go
index 257c845443..84c8d38fc2 100644
--- a/storage/local/doubledelta.go
+++ b/storage/local/doubledelta.go
@@ -208,15 +208,17 @@ func (c doubleDeltaEncodedChunk) firstTime() model.Time {
 // newIterator implements chunk.
 func (c *doubleDeltaEncodedChunk) newIterator() chunkIterator {
 	return &doubleDeltaEncodedChunkIterator{
-		c:      *c,
-		len:    c.len(),
-		baseT:  c.baseTime(),
-		baseΔT: c.baseTimeDelta(),
-		baseV:  c.baseValue(),
-		baseΔV: c.baseValueDelta(),
-		tBytes: c.timeBytes(),
-		vBytes: c.valueBytes(),
-		isInt:  c.isInt(),
+		c:         *c,
+		len:       c.len(),
+		baseT:     c.baseTime(),
+		baseΔT:    c.baseTimeDelta(),
+		baseV:     c.baseValue(),
+		baseΔV:    c.baseValueDelta(),
+		tBytes:    c.timeBytes(),
+		vBytes:    c.valueBytes(),
+		isInt:     c.isInt(),
+		pos:       -1,
+		lastValue: ZeroSamplePair,
 	}
 }
 
@@ -417,132 +419,95 @@ type doubleDeltaEncodedChunkIterator struct {
 	baseV, baseΔV  model.SampleValue
 	tBytes, vBytes deltaBytes
 	isInt          bool
+	pos            int
+	lastValue      model.SamplePair
+	lastErr        error
 }
 
-// length implements chunkIterator.
-func (it *doubleDeltaEncodedChunkIterator) length() int { return it.len }
+// lastTimestamp implements chunkIterator.
+func (it *doubleDeltaEncodedChunkIterator) lastTimestamp() (model.Time, error) {
+	return it.timestampAtIndex(it.len - 1), it.lastErr
+}
 
 // valueAtOrBeforeTime implements chunkIterator.
 func (it *doubleDeltaEncodedChunkIterator) valueAtOrBeforeTime(t model.Time) (model.SamplePair, error) {
-	var lastErr error
 	i := sort.Search(it.len, func(i int) bool {
-		ts, err := it.timestampAtIndex(i)
-		if err != nil {
-			lastErr = err
-		}
-		return ts.After(t)
+		return it.timestampAtIndex(i).After(t)
 	})
-	if i == 0 || lastErr != nil {
-		return ZeroSamplePair, lastErr
+	if i == 0 || it.lastErr != nil {
+		return ZeroSamplePair, it.lastErr
 	}
-	ts, err := it.timestampAtIndex(i - 1)
-	if err != nil {
-		return ZeroSamplePair, err
+	it.pos = i - 1
+	it.lastValue = model.SamplePair{
+		Timestamp: it.timestampAtIndex(i - 1),
+		Value:     it.sampleValueAtIndex(i - 1),
 	}
-	v, err := it.sampleValueAtIndex(i - 1)
-	if err != nil {
-		return ZeroSamplePair, err
-	}
-	return model.SamplePair{Timestamp: ts, Value: v}, nil
+	return it.lastValue, it.lastErr
 }
 
 // rangeValues implements chunkIterator.
 func (it *doubleDeltaEncodedChunkIterator) rangeValues(in metric.Interval) ([]model.SamplePair, error) {
-	var lastErr error
-
 	oldest := sort.Search(it.len, func(i int) bool {
-		t, err := it.timestampAtIndex(i)
-		if err != nil {
-			lastErr = err
-		}
-		return !t.Before(in.OldestInclusive)
+		return !it.timestampAtIndex(i).Before(in.OldestInclusive)
 	})
-
 	newest := sort.Search(it.len, func(i int) bool {
-		t, err := it.timestampAtIndex(i)
-		if err != nil {
-			lastErr = err
-		}
-		return t.After(in.NewestInclusive)
+		return it.timestampAtIndex(i).After(in.NewestInclusive)
 	})
-
-	if oldest == it.len || lastErr != nil {
-		return nil, lastErr
+	if oldest == it.len || it.lastErr != nil {
+		return nil, it.lastErr
 	}
 
 	result := make([]model.SamplePair, 0, newest-oldest)
 	for i := oldest; i < newest; i++ {
-		t, err := it.timestampAtIndex(i)
-		if err != nil {
-			return nil, err
+		it.pos = i
+		it.lastValue = model.SamplePair{
+			Timestamp: it.timestampAtIndex(i),
+			Value:     it.sampleValueAtIndex(i),
 		}
-		v, err := it.sampleValueAtIndex(i)
-		if err != nil {
-			return nil, err
-		}
-		result = append(result, model.SamplePair{Timestamp: t, Value: v})
+		result = append(result, it.lastValue)
 	}
-	return result, nil
+	return result, it.lastErr
 }
 
 // contains implements chunkIterator.
 func (it *doubleDeltaEncodedChunkIterator) contains(t model.Time) (bool, error) {
-	lastT, err := it.timestampAtIndex(it.len - 1)
-	if err != nil {
-		return false, err
+	return !t.Before(it.baseT) && !t.After(it.timestampAtIndex(it.len-1)), it.lastErr
+}
+
+// scan implements chunkIterator.
+func (it *doubleDeltaEncodedChunkIterator) scan() bool {
+	it.pos++
+	if it.pos >= it.len {
+		return false
 	}
-	return !t.Before(it.baseT) && !t.After(lastT), nil
+	it.lastValue = model.SamplePair{
+		Timestamp: it.timestampAtIndex(it.pos),
+		Value:     it.sampleValueAtIndex(it.pos),
+	}
+	return it.lastErr == nil
 }
 
-// values implements chunkIterator.
-func (it *doubleDeltaEncodedChunkIterator) values() <-chan struct {
-	model.SamplePair
-	error
-} {
-	valuesChan := make(chan struct {
-		model.SamplePair
-		error
-	})
-	go func() {
-		for i := 0; i < it.len; i++ {
-			t, err := it.timestampAtIndex(i)
-			if err != nil {
-				valuesChan <- struct {
-					model.SamplePair
-					error
-				}{ZeroSamplePair, err}
-				break
-			}
-			v, err := it.sampleValueAtIndex(i)
-			if err != nil {
-				valuesChan <- struct {
-					model.SamplePair
-					error
-				}{ZeroSamplePair, err}
-				break
-			}
-			valuesChan <- struct {
-				model.SamplePair
-				error
-			}{model.SamplePair{Timestamp: t, Value: v}, nil}
-		}
-		close(valuesChan)
-	}()
-	return valuesChan
+// value implements chunkIterator.
+func (it *doubleDeltaEncodedChunkIterator) value() model.SamplePair {
+	return it.lastValue
 }
 
-// timestampAtIndex implements chunkIterator.
-func (it *doubleDeltaEncodedChunkIterator) timestampAtIndex(idx int) (model.Time, error) {
+// err implements chunkIterator.
+func (it *doubleDeltaEncodedChunkIterator) err() error {
+	return it.lastErr
+}
+
+func (it *doubleDeltaEncodedChunkIterator) timestampAtIndex(idx int) model.Time {
 	if idx == 0 {
-		return it.baseT, nil
+		return it.baseT
 	}
 	if idx == 1 {
 		// If time bytes are at d8, the time is saved directly rather
 		// than as a difference.
 		if it.tBytes == d8 {
-			return it.baseΔT, nil
+			return it.baseΔT
 		}
-		return it.baseT + it.baseΔT, nil
+		return it.baseT + it.baseΔT
 	}
 
 	offset := doubleDeltaHeaderBytes + (idx-2)*int(it.tBytes+it.vBytes)
@@ -551,40 +516,35 @@ func (it *doubleDeltaEncodedChunkIterator) timestampAtIndex(idx int) (model.Time
 	case d1:
 		return it.baseT +
 			model.Time(idx)*it.baseΔT +
-			model.Time(int8(it.c[offset])), nil
+			model.Time(int8(it.c[offset]))
 	case d2:
 		return it.baseT +
 			model.Time(idx)*it.baseΔT +
-			model.Time(int16(binary.LittleEndian.Uint16(it.c[offset:]))), nil
+			model.Time(int16(binary.LittleEndian.Uint16(it.c[offset:])))
 	case d4:
 		return it.baseT +
 			model.Time(idx)*it.baseΔT +
-			model.Time(int32(binary.LittleEndian.Uint32(it.c[offset:]))), nil
+			model.Time(int32(binary.LittleEndian.Uint32(it.c[offset:])))
 	case d8:
 		// Take absolute value for d8.
-		return model.Time(binary.LittleEndian.Uint64(it.c[offset:])), nil
+		return model.Time(binary.LittleEndian.Uint64(it.c[offset:]))
 	default:
-		return 0, fmt.Errorf("invalid number of bytes for time delta: %d", it.tBytes)
+		it.lastErr = fmt.Errorf("invalid number of bytes for time delta: %d", it.tBytes)
 	}
+	return model.Earliest
 }
 
-// lastTimestamp implements chunkIterator.
-func (it *doubleDeltaEncodedChunkIterator) lastTimestamp() (model.Time, error) {
-	return it.timestampAtIndex(it.len - 1)
-}
-
-// sampleValueAtIndex implements chunkIterator.
-func (it *doubleDeltaEncodedChunkIterator) sampleValueAtIndex(idx int) (model.SampleValue, error) {
+func (it *doubleDeltaEncodedChunkIterator) sampleValueAtIndex(idx int) model.SampleValue {
 	if idx == 0 {
-		return it.baseV, nil
+		return it.baseV
 	}
 	if idx == 1 {
 		// If value bytes are at d8, the value is saved directly rather
 		// than as a difference.
 		if it.vBytes == d8 {
-			return it.baseΔV, nil
+			return it.baseΔV
 		}
-		return it.baseV + it.baseΔV, nil
+		return it.baseV + it.baseΔV
 	}
 
 	offset := doubleDeltaHeaderBytes + (idx-2)*int(it.tBytes+it.vBytes) + int(it.tBytes)
@@ -593,39 +553,35 @@ func (it *doubleDeltaEncodedChunkIterator) sampleValueAtIndex(idx int) (model.Sa
 		switch it.vBytes {
 		case d0:
 			return it.baseV +
-				model.SampleValue(idx)*it.baseΔV, nil
+				model.SampleValue(idx)*it.baseΔV
 		case d1:
 			return it.baseV +
 				model.SampleValue(idx)*it.baseΔV +
-				model.SampleValue(int8(it.c[offset])), nil
+				model.SampleValue(int8(it.c[offset]))
 		case d2:
 			return it.baseV +
 				model.SampleValue(idx)*it.baseΔV +
-				model.SampleValue(int16(binary.LittleEndian.Uint16(it.c[offset:]))), nil
+				model.SampleValue(int16(binary.LittleEndian.Uint16(it.c[offset:])))
 		case d4:
 			return it.baseV +
 				model.SampleValue(idx)*it.baseΔV +
-				model.SampleValue(int32(binary.LittleEndian.Uint32(it.c[offset:]))), nil
+				model.SampleValue(int32(binary.LittleEndian.Uint32(it.c[offset:])))
 		// No d8 for ints.
 		default:
-			return 0, fmt.Errorf("invalid number of bytes for integer delta: %d", it.vBytes)
+			it.lastErr = fmt.Errorf("invalid number of bytes for integer delta: %d", it.vBytes)
 		}
 	} else {
 		switch it.vBytes {
 		case d4:
 			return it.baseV +
 				model.SampleValue(idx)*it.baseΔV +
-				model.SampleValue(math.Float32frombits(binary.LittleEndian.Uint32(it.c[offset:]))), nil
+				model.SampleValue(math.Float32frombits(binary.LittleEndian.Uint32(it.c[offset:])))
 		case d8:
 			// Take absolute value for d8.
-			return model.SampleValue(math.Float64frombits(binary.LittleEndian.Uint64(it.c[offset:]))), nil
+			return model.SampleValue(math.Float64frombits(binary.LittleEndian.Uint64(it.c[offset:])))
 		default:
-			return 0, fmt.Errorf("invalid number of bytes for floating point delta: %d", it.vBytes)
+			it.lastErr = fmt.Errorf("invalid number of bytes for floating point delta: %d", it.vBytes)
 		}
 	}
-}
-
-// lastSampleValue implements chunkIterator.
-func (it *doubleDeltaEncodedChunkIterator) lastSampleValue() (model.SampleValue, error) {
-	return it.sampleValueAtIndex(it.len - 1)
+	return 0
 }
diff --git a/storage/local/persistence_test.go b/storage/local/persistence_test.go
index e1894032af..e2da778035 100644
--- a/storage/local/persistence_test.go
+++ b/storage/local/persistence_test.go
@@ -82,14 +82,14 @@ func buildTestChunks(t *testing.T, encoding chunkEncoding) map[model.Fingerprint
 }
 
 func chunksEqual(c1, c2 chunk) bool {
-	values2 := c2.newIterator().values()
-	for v1 := range c1.newIterator().values() {
-		v2 := <-values2
-		if !(v1 == v2) {
+	it1 := c1.newIterator()
+	it2 := c2.newIterator()
+	for it1.scan() && it2.scan() {
+		if !(it1.value() == it2.value()) {
 			return false
 		}
 	}
-	return true
+	return it1.err() == nil && it2.err() == nil
 }
 
 func testPersistLoadDropChunks(t *testing.T, encoding chunkEncoding) {
diff --git a/storage/local/storage_test.go b/storage/local/storage_test.go
index 97fa450ba7..5fcb39c435 100644
--- a/storage/local/storage_test.go
+++ b/storage/local/storage_test.go
@@ -692,11 +692,12 @@ func testChunk(t *testing.T, encoding chunkEncoding) {
 			if cd.isEvicted() {
 				continue
 			}
-			for sample := range cd.c.newIterator().values() {
-				if sample.error != nil {
-					t.Error(sample.error)
-				}
-				values = append(values, sample.SamplePair)
+			it := cd.c.newIterator()
+			for it.scan() {
+				values = append(values, it.value())
+			}
+			if it.err() != nil {
+				t.Error(it.err())
 			}
 		}