diff --git a/compact.go b/compact.go
index 412a24788..73018ca20 100644
--- a/compact.go
+++ b/compact.go
@@ -177,7 +177,7 @@ func (c *compactor) compact(dir string, blocks ...Block) (err error) {
 	}
 
 	indexw := newIndexWriter(indexf)
-	chunkw := newSeriesWriter(chunkf, indexw)
+	chunkw := newChunkWriter(chunkf)
 
 	if err = c.write(dir, blocks, indexw, chunkw); err != nil {
 		return errors.Wrap(err, "write compaction")
@@ -204,7 +204,7 @@ func (c *compactor) compact(dir string, blocks ...Block) (err error) {
 	return nil
 }
 
-func (c *compactor) write(dir string, blocks []Block, indexw IndexWriter, chunkw SeriesWriter) error {
+func (c *compactor) write(dir string, blocks []Block, indexw IndexWriter, chunkw ChunkWriter) error {
 	var set compactionSet
 
 	for i, b := range blocks {
@@ -238,10 +238,12 @@ func (c *compactor) write(dir string, blocks []Block, indexw IndexWriter, chunkw
 
 	for set.Next() {
 		lset, chunks := set.At()
-		if err := chunkw.WriteSeries(i, lset, chunks); err != nil {
+		if err := chunkw.WriteChunks(chunks...); err != nil {
 			return err
 		}
 
+		indexw.AddSeries(i, lset, chunks...)
+
 		meta.Stats.NumChunks += uint64(len(chunks))
 		meta.Stats.NumSeries++
 
diff --git a/writer.go b/writer.go
index 2229ff02a..6b4e31deb 100644
--- a/writer.go
+++ b/writer.go
@@ -25,12 +25,13 @@ const (
 
 const compactionPageBytes = minSectorSize * 64
 
-// SeriesWriter serializes a time block of chunked series data.
-type SeriesWriter interface {
-	// WriteSeries writes the time series data chunks for a single series.
-	// The reference is used to resolve the correct series in the written index.
-	// It only has to be valid for the duration of the write.
-	WriteSeries(ref uint32, l labels.Labels, chunks []ChunkMeta) error
+// ChunkWriter serializes a time block of chunked series data.
+type ChunkWriter interface {
+	// WriteChunks writes several chunks. The data field of the ChunkMetas
+	// must be populated.
+	// After returning successfully, the Ref fields in the ChunkMetas
+	// is set and can be used to retrieve the chunks from the written data.
+	WriteChunks(chunks ...ChunkMeta) error
 
 	// Size returns the size of the data written so far.
 	Size() int64
@@ -40,35 +41,32 @@ type SeriesWriter interface {
 	Close() error
 }
 
-// seriesWriter implements the SeriesWriter interface for the standard
+// chunkWriter implements the ChunkWriter interface for the standard
 // serialization format.
-type seriesWriter struct {
+type chunkWriter struct {
 	ow    io.Writer
 	w     *bufio.Writer
 	n     int64
 	c     int
 	crc32 hash.Hash
-
-	index IndexWriter
 }
 
-func newSeriesWriter(w io.Writer, index IndexWriter) *seriesWriter {
-	return &seriesWriter{
+func newChunkWriter(w io.Writer) *chunkWriter {
+	return &chunkWriter{
 		ow:    w,
 		w:     bufio.NewWriterSize(w, 1*1024*1024),
 		n:     0,
 		crc32: crc32.New(crc32.MakeTable(crc32.Castagnoli)),
-		index: index,
 	}
 }
 
-func (w *seriesWriter) write(wr io.Writer, b []byte) error {
+func (w *chunkWriter) write(wr io.Writer, b []byte) error {
 	n, err := wr.Write(b)
 	w.n += int64(n)
 	return err
 }
 
-func (w *seriesWriter) writeMeta() error {
+func (w *chunkWriter) writeMeta() error {
 	b := [8]byte{}
 
 	binary.BigEndian.PutUint32(b[:4], MagicSeries)
@@ -77,7 +75,7 @@ func (w *seriesWriter) writeMeta() error {
 	return w.write(w.w, b[:])
 }
 
-func (w *seriesWriter) WriteSeries(ref uint32, lset labels.Labels, chks []ChunkMeta) error {
+func (w *chunkWriter) WriteChunks(chks ...ChunkMeta) error {
 	// Initialize with meta data.
 	if w.n == 0 {
 		if err := w.writeMeta(); err != nil {
@@ -122,18 +120,14 @@ func (w *seriesWriter) WriteSeries(ref uint32, lset labels.Labels, chks []ChunkM
 	if err := w.write(w.w, w.crc32.Sum(nil)); err != nil {
 		return err
 	}
-
-	if w.index != nil {
-		w.index.AddSeries(ref, lset, chks...)
-	}
 	return nil
 }
 
-func (w *seriesWriter) Size() int64 {
+func (w *chunkWriter) Size() int64 {
 	return w.n
 }
 
-func (w *seriesWriter) Close() error {
+func (w *chunkWriter) Close() error {
 	// Initialize block in case no data was written to it.
 	if w.n == 0 {
 		if err := w.writeMeta(); err != nil {