diff --git a/block.go b/block.go
index ca7c48f46..35548f62e 100644
--- a/block.go
+++ b/block.go
@@ -130,11 +130,11 @@ func newPersistedBlock(dir string) (*persistedBlock, error) {
 		return nil, errors.Wrap(err, "open index file")
 	}
 
-	sr, err := newSeriesReader(chunksf.b)
+	sr, err := newSeriesReader([][]byte{chunksf.b})
 	if err != nil {
 		return nil, errors.Wrap(err, "create series reader")
 	}
-	ir, err := newIndexReader(sr, indexf.b)
+	ir, err := newIndexReader(indexf.b)
 	if err != nil {
 		return nil, errors.Wrap(err, "create index reader")
 	}
diff --git a/head.go b/head.go
index 33bcb7088..d9ab2944c 100644
--- a/head.go
+++ b/head.go
@@ -364,14 +364,17 @@ type headSeriesReader struct {
 }
 
 // Chunk returns the chunk for the reference number.
-func (h *headSeriesReader) Chunk(ref uint32) (chunks.Chunk, error) {
+func (h *headSeriesReader) Chunk(ref uint64) (chunks.Chunk, error) {
 	h.mtx.RLock()
 	defer h.mtx.RUnlock()
 
+	si := ref >> 32
+	ci := (ref << 32) >> 32
+
 	c := &safeChunk{
-		Chunk: h.series[ref>>8].chunks[int((ref<<24)>>24)].chunk,
-		s:     h.series[ref>>8],
-		i:     int((ref << 24) >> 24),
+		Chunk: h.series[si].chunks[ci].chunk,
+		s:     h.series[si],
+		i:     int(ci),
 	}
 	return c, nil
 }
@@ -440,7 +443,7 @@ func (h *headIndexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error)
 		metas = append(metas, ChunkMeta{
 			MinTime: c.minTime,
 			MaxTime: c.maxTime,
-			Ref:     (ref << 8) | uint32(i),
+			Ref:     (uint64(ref) << 32) | uint64(i),
 		})
 	}
 
diff --git a/querier.go b/querier.go
index df17ad270..c09bab885 100644
--- a/querier.go
+++ b/querier.go
@@ -491,7 +491,7 @@ type chunkSeries struct {
 
 	// chunk is a function that retrieves chunks based on a reference
 	// number contained in the chunk meta information.
-	chunk func(ref uint32) (chunks.Chunk, error)
+	chunk func(ref uint64) (chunks.Chunk, error)
 }
 
 func (s *chunkSeries) Labels() labels.Labels {
diff --git a/reader.go b/reader.go
index a49fb794b..630c11a99 100644
--- a/reader.go
+++ b/reader.go
@@ -13,32 +13,45 @@ import (
 // SeriesReader provides reading access of serialized time series data.
 type SeriesReader interface {
 	// Chunk returns the series data chunk with the given reference.
-	Chunk(ref uint32) (chunks.Chunk, error)
+	Chunk(ref uint64) (chunks.Chunk, error)
 }
 
 // seriesReader implements a SeriesReader for a serialized byte stream
 // of series data.
 type seriesReader struct {
-	// The underlying byte slice holding the encoded series data.
-	b []byte
+	// The underlying bytes holding the encoded series data.
+	bs [][]byte
 }
 
-func newSeriesReader(b []byte) (*seriesReader, error) {
-	if len(b) < 4 {
-		return nil, errors.Wrap(errInvalidSize, "index header")
+func newSeriesReader(bs [][]byte) (*seriesReader, error) {
+	s := &seriesReader{bs: bs}
+
+	for i, b := range bs {
+		if len(b) < 4 {
+			return nil, errors.Wrapf(errInvalidSize, "validate magic in segment %d", i)
+		}
+		// Verify magic number.
+		if m := binary.BigEndian.Uint32(b[:4]); m != MagicSeries {
+			return nil, fmt.Errorf("invalid magic number %x", m)
+		}
 	}
-	// Verify magic number.
-	if m := binary.BigEndian.Uint32(b[:4]); m != MagicSeries {
-		return nil, fmt.Errorf("invalid magic number %x", m)
-	}
-	return &seriesReader{b: b}, nil
+	return s, nil
 }
 
-func (s *seriesReader) Chunk(offset uint32) (chunks.Chunk, error) {
-	if int(offset) > len(s.b) {
-		return nil, errors.Errorf("offset %d beyond data size %d", offset, len(s.b))
+func (s *seriesReader) Chunk(ref uint64) (chunks.Chunk, error) {
+	var (
+		seq = int(ref >> 32)
+		off = int((ref << 32) >> 32)
+	)
+	if seq >= len(s.bs) {
+		return nil, errors.Errorf("reference sequence %d out of range", seq)
 	}
-	b := s.b[offset:]
+	b := s.bs[seq]
+
+	if int(off) >= len(b) {
+		return nil, errors.Errorf("offset %d beyond data size %d", off, len(b))
+	}
+	b = b[off:]
 
 	l, n := binary.Uvarint(b)
 	if n < 0 {
@@ -78,8 +91,6 @@ type StringTuples interface {
 }
 
 type indexReader struct {
-	series SeriesReader
-
 	// The underlying byte slice holding the encoded series data.
 	b []byte
 
@@ -93,14 +104,11 @@ var (
 	errInvalidFlag = fmt.Errorf("invalid flag")
 )
 
-func newIndexReader(s SeriesReader, b []byte) (*indexReader, error) {
+func newIndexReader(b []byte) (*indexReader, error) {
 	if len(b) < 4 {
 		return nil, errors.Wrap(errInvalidSize, "index header")
 	}
-	r := &indexReader{
-		series: s,
-		b:      b,
-	}
+	r := &indexReader{b: b}
 
 	// Verify magic number.
 	if m := binary.BigEndian.Uint32(b[:4]); m != MagicIndex {
@@ -299,7 +307,7 @@ func (r *indexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error) {
 		b = b[n:]
 
 		chunks = append(chunks, ChunkMeta{
-			Ref:     uint32(o),
+			Ref:     o,
 			MinTime: firstTime,
 			MaxTime: lastTime,
 		})
diff --git a/writer.go b/writer.go
index 86bb75274..2229ff02a 100644
--- a/writer.go
+++ b/writer.go
@@ -103,7 +103,7 @@ func (w *seriesWriter) WriteSeries(ref uint32, lset labels.Labels, chks []ChunkM
 	for i := range chks {
 		chk := &chks[i]
 
-		chk.Ref = uint32(w.n)
+		chk.Ref = uint64(w.n)
 
 		n = binary.PutUvarint(b[:], uint64(len(chk.Chunk.Bytes())))
 
@@ -148,7 +148,7 @@ type ChunkMeta struct {
 	// Ref and Chunk hold either a reference that can be used to retrieve
 	// chunk data or the data itself.
 	// Generally, only one of them is set.
-	Ref   uint32
+	Ref   uint64
 	Chunk chunks.Chunk
 
 	MinTime, MaxTime int64 // time range the data covers