diff --git a/pkg/chunkenc/memchunk.go b/pkg/chunkenc/memchunk.go
index e297a482da2e..362df2c89338 100644
--- a/pkg/chunkenc/memchunk.go
+++ b/pkg/chunkenc/memchunk.go
@@ -44,6 +44,20 @@ const (
 	defaultBlockSize = 256 * 1024
 )
 
+type HeadBlockFmt byte
+
+func (f HeadBlockFmt) Byte() byte { return byte(f) }
+
+const (
+	_ HeadBlockFmt = iota
+	// placeholders to start splitting chunk formats vs head block
+	// fmts at v3
+	_
+	_
+	OrderedHeadBlockFmt
+	UnorderedHeadBlockFmt
+)
+
 var magicNumber = uint32(0x12EE56A)
 
 // The table gets initialized with sync.Once but may still cause a race
@@ -74,7 +88,7 @@ type MemChunk struct {
 	cutBlockSize int
 
 	// Current in-mem block being appended to.
-	head *headBlock
+	head HeadBlock
 
 	// the chunk format default to v2
 	format   byte
@@ -102,11 +116,17 @@ type headBlock struct {
 	mint, maxt int64
 }
 
-func (hb *headBlock) isEmpty() bool {
+func (hb *headBlock) Format() HeadBlockFmt { return OrderedHeadBlockFmt }
+
+func (hb *headBlock) IsEmpty() bool {
 	return len(hb.entries) == 0
 }
 
-func (hb *headBlock) clear() {
+func (hb *headBlock) Entries() int { return len(hb.entries) }
+
+func (hb *headBlock) UncompressedSize() int { return hb.size }
+
+func (hb *headBlock) Reset() {
 	if hb.entries != nil {
 		hb.entries = hb.entries[:0]
 	}
@@ -115,8 +135,10 @@ func (hb *headBlock) clear() {
 	hb.maxt = 0
 }
 
-func (hb *headBlock) append(ts int64, line string) error {
-	if !hb.isEmpty() && hb.maxt > ts {
+func (hb *headBlock) Bounds() (int64, int64) { return hb.mint, hb.maxt }
+
+func (hb *headBlock) Append(ts int64, line string) error {
+	if !hb.IsEmpty() && hb.maxt > ts {
 		return ErrOutOfOrder
 	}
 
@@ -130,7 +152,7 @@ func (hb *headBlock) append(ts int64, line string) error {
 	return nil
 }
 
-func (hb *headBlock) serialise(pool WriterPool) ([]byte, error) {
+func (hb *headBlock) Serialise(pool WriterPool) ([]byte, error) {
 	inBuf := serializeBytesBufferPool.Get().(*bytes.Buffer)
 	defer func() {
 		inBuf.Reset()
@@ -164,14 +186,14 @@ func (hb *headBlock) serialise(pool WriterPool) ([]byte, error) {
 // CheckpointBytes serializes a headblock to []byte. This is used by the WAL checkpointing,
 // which does not want to mutate a chunk by cutting it (otherwise risking content address changes), but
 // needs to serialize/deserialize the data to disk to ensure data durability.
-func (hb *headBlock) CheckpointBytes(version byte, b []byte) ([]byte, error) {
+func (hb *headBlock) CheckpointBytes(b []byte) ([]byte, error) {
 	buf := bytes.NewBuffer(b[:0])
-	err := hb.CheckpointTo(version, buf)
+	err := hb.CheckpointTo(buf)
 	return buf.Bytes(), err
 }
 
 // CheckpointSize returns the estimated size of the headblock checkpoint.
-func (hb *headBlock) CheckpointSize(version byte) int {
+func (hb *headBlock) CheckpointSize() int {
 	size := 1                                                                 // version
 	size += binary.MaxVarintLen32 * 2                                         // total entries + total size
 	size += binary.MaxVarintLen64 * 2                                         // mint,maxt
@@ -184,13 +206,13 @@ func (hb *headBlock) CheckpointSize(version byte) int {
 }
 
 // CheckpointTo serializes a headblock to a `io.Writer`. see `CheckpointBytes`.
-func (hb *headBlock) CheckpointTo(version byte, w io.Writer) error {
+func (hb *headBlock) CheckpointTo(w io.Writer) error {
 	eb := EncodeBufferPool.Get().(*encbuf)
 	defer EncodeBufferPool.Put(eb)
 
 	eb.reset()
 
-	eb.putByte(version)
+	eb.putByte(byte(hb.Format()))
 	_, err := w.Write(eb.get())
 	if err != nil {
 		return errors.Wrap(err, "write headBlock version")
@@ -225,7 +247,7 @@ func (hb *headBlock) CheckpointTo(version byte, w io.Writer) error {
 	return nil
 }
 
-func (hb *headBlock) FromCheckpoint(b []byte) error {
+func (hb *headBlock) LoadBytes(b []byte) error {
 	if len(b) < 1 {
 		return nil
 	}
@@ -267,6 +289,20 @@ func (hb *headBlock) FromCheckpoint(b []byte) error {
 	return nil
 }
 
+func (hb *headBlock) Convert(version HeadBlockFmt) (HeadBlock, error) {
+	if version < UnorderedHeadBlockFmt {
+		return hb, nil
+	}
+	out := newUnorderedHeadBlock()
+
+	for _, e := range hb.entries {
+		if err := out.Append(e.t, e.s); err != nil {
+			return nil, err
+		}
+	}
+	return out, nil
+}
+
 type entry struct {
 	t int64
 	s string
@@ -511,11 +547,11 @@ func (c *MemChunk) SerializeForCheckpointTo(chk, head io.Writer) error {
 		return err
 	}
 
-	if c.head.isEmpty() {
+	if c.head.IsEmpty() {
 		return nil
 	}
 
-	err = c.head.CheckpointTo(c.format, head)
+	err = c.head.CheckpointTo(head)
 	if err != nil {
 		return err
 	}
@@ -524,7 +560,7 @@ func (c *MemChunk) SerializeForCheckpointTo(chk, head io.Writer) error {
 }
 
 func (c *MemChunk) CheckpointSize() (chunk, head int) {
-	return c.BytesSize(), c.head.CheckpointSize(c.format)
+	return c.BytesSize(), c.head.CheckpointSize()
 }
 
 func MemchunkFromCheckpoint(chk, head []byte, blockSize int, targetSize int) (*MemChunk, error) {
@@ -532,7 +568,7 @@ func MemchunkFromCheckpoint(chk, head []byte, blockSize int, targetSize int) (*M
 	if err != nil {
 		return nil, err
 	}
-	return mc, mc.head.FromCheckpoint(head)
+	return mc, mc.head.LoadBytes(head)
 }
 
 // Encoding implements Chunk.
@@ -547,9 +583,7 @@ func (c *MemChunk) Size() int {
 		ne += blk.numEntries
 	}
 
-	if !c.head.isEmpty() {
-		ne += len(c.head.entries)
-	}
+	ne += c.head.Entries()
 
 	return ne
 }
@@ -564,7 +598,7 @@ func (c *MemChunk) SpaceFor(e *logproto.Entry) bool {
 	if c.targetSize > 0 {
 		// This is looking to see if the uncompressed lines will fit which is not
 		// a great check, but it will guarantee we are always under the target size
-		newHBSize := c.head.size + len(e.Line)
+		newHBSize := c.head.UncompressedSize() + len(e.Line)
 		return (c.cutBlockSize + newHBSize) < c.targetSize
 	}
 	// if targetSize is not defined, default to the original behavior of fixed blocks per chunk
@@ -575,9 +609,7 @@ func (c *MemChunk) SpaceFor(e *logproto.Entry) bool {
 func (c *MemChunk) UncompressedSize() int {
 	size := 0
 
-	if !c.head.isEmpty() {
-		size += c.head.size
-	}
+	size += c.head.UncompressedSize()
 
 	for _, b := range c.blocks {
 		size += b.uncompressedSize
@@ -590,9 +622,7 @@ func (c *MemChunk) UncompressedSize() int {
 func (c *MemChunk) CompressedSize() int {
 	size := 0
 	// Better to account for any uncompressed data than ignore it even though this isn't accurate.
-	if !c.head.isEmpty() {
-		size += c.head.size
-	}
+	size += c.head.UncompressedSize()
 	size += c.cutBlockSize
 	return size
 }
@@ -612,15 +642,15 @@ func (c *MemChunk) Append(entry *logproto.Entry) error {
 
 	// If the head block is empty but there are cut blocks, we have to make
 	// sure the new entry is not out of order compared to the previous block
-	if c.head.isEmpty() && len(c.blocks) > 0 && c.blocks[len(c.blocks)-1].maxt > entryTimestamp {
+	if c.head.IsEmpty() && len(c.blocks) > 0 && c.blocks[len(c.blocks)-1].maxt > entryTimestamp {
 		return ErrOutOfOrder
 	}
 
-	if err := c.head.append(entryTimestamp, entry.Line); err != nil {
+	if err := c.head.Append(entryTimestamp, entry.Line); err != nil {
 		return err
 	}
 
-	if c.head.size >= c.blockSize {
+	if c.head.UncompressedSize() >= c.blockSize {
 		return c.cut()
 	}
 
@@ -635,44 +665,41 @@ func (c *MemChunk) Close() error {
 
 // cut a new block and add it to finished blocks.
 func (c *MemChunk) cut() error {
-	if c.head.isEmpty() {
+	if c.head.IsEmpty() {
 		return nil
 	}
 
-	b, err := c.head.serialise(getWriterPool(c.encoding))
+	b, err := c.head.Serialise(getWriterPool(c.encoding))
 	if err != nil {
 		return err
 	}
 
+	mint, maxt := c.head.Bounds()
 	c.blocks = append(c.blocks, block{
 		b:                b,
-		numEntries:       len(c.head.entries),
-		mint:             c.head.mint,
-		maxt:             c.head.maxt,
-		uncompressedSize: c.head.size,
+		numEntries:       c.head.Entries(),
+		mint:             mint,
+		maxt:             maxt,
+		uncompressedSize: c.head.UncompressedSize(),
 	})
 
 	c.cutBlockSize += len(b)
 
-	c.head.clear()
+	c.head.Reset()
 	return nil
 }
 
 // Bounds implements Chunk.
 func (c *MemChunk) Bounds() (fromT, toT time.Time) {
-	var from, to int64
-	if len(c.blocks) > 0 {
-		from = c.blocks[0].mint
-		to = c.blocks[len(c.blocks)-1].maxt
-	}
+	from, to := c.head.Bounds()
 
-	if !c.head.isEmpty() {
-		if from == 0 || from > c.head.mint {
-			from = c.head.mint
+	// need to check all the blocks in case they overlap
+	for _, b := range c.blocks {
+		if from == 0 || from > b.mint {
+			from = b.mint
 		}
-
-		if to < c.head.maxt {
-			to = c.head.maxt
+		if to < b.maxt {
+			to = b.maxt
 		}
 	}
 
@@ -692,8 +719,8 @@ func (c *MemChunk) Iterator(ctx context.Context, mintT, maxtT time.Time, directi
 		blockItrs = append(blockItrs, encBlock{c.encoding, b}.Iterator(ctx, pipeline))
 	}
 
-	if !c.head.isEmpty() {
-		headIterator = c.head.iterator(ctx, direction, mint, maxt, pipeline)
+	if !c.head.IsEmpty() {
+		headIterator = c.head.Iterator(ctx, direction, mint, maxt, pipeline)
 	}
 
 	if direction == logproto.FORWARD {
@@ -743,8 +770,8 @@ func (c *MemChunk) SampleIterator(ctx context.Context, from, through time.Time,
 		its = append(its, encBlock{c.encoding, b}.SampleIterator(ctx, extractor))
 	}
 
-	if !c.head.isEmpty() {
-		its = append(its, c.head.sampleIterator(ctx, mint, maxt, extractor))
+	if !c.head.IsEmpty() {
+		its = append(its, c.head.SampleIterator(ctx, mint, maxt, extractor))
 	}
 
 	return iter.NewTimeRangedSampleIterator(
@@ -837,8 +864,8 @@ func (b block) MaxTime() int64 {
 	return b.maxt
 }
 
-func (hb *headBlock) iterator(ctx context.Context, direction logproto.Direction, mint, maxt int64, pipeline log.StreamPipeline) iter.EntryIterator {
-	if hb.isEmpty() || (maxt < hb.mint || hb.maxt < mint) {
+func (hb *headBlock) Iterator(ctx context.Context, direction logproto.Direction, mint, maxt int64, pipeline log.StreamPipeline) iter.EntryIterator {
+	if hb.IsEmpty() || (maxt < hb.mint || hb.maxt < mint) {
 		return iter.NoopIterator
 	}
 
@@ -895,8 +922,8 @@ func (hb *headBlock) iterator(ctx context.Context, direction logproto.Direction,
 	return iter.NewStreamsIterator(ctx, streamsResult, direction)
 }
 
-func (hb *headBlock) sampleIterator(ctx context.Context, mint, maxt int64, extractor log.StreamSampleExtractor) iter.SampleIterator {
-	if hb.isEmpty() || (maxt < hb.mint || hb.maxt < mint) {
+func (hb *headBlock) SampleIterator(ctx context.Context, mint, maxt int64, extractor log.StreamSampleExtractor) iter.SampleIterator {
+	if hb.IsEmpty() || (maxt < hb.mint || hb.maxt < mint) {
 		return iter.NoopIterator
 	}
 	chunkStats := stats.GetChunkData(ctx)
diff --git a/pkg/chunkenc/memchunk_test.go b/pkg/chunkenc/memchunk_test.go
index ed457315c40c..fb6173f5fca2 100644
--- a/pkg/chunkenc/memchunk_test.go
+++ b/pkg/chunkenc/memchunk_test.go
@@ -283,9 +283,9 @@ func TestRoundtripV3(t *testing.T) {
 			require.Nil(t, err)
 
 			// have to populate then clear the head block or fail comparing against nil vs zero values
-			err = r.head.append(1, "1")
+			err = r.head.Append(1, "1")
 			require.Nil(t, err)
-			r.head.clear()
+			r.head.Reset()
 
 			require.Equal(t, c, r)
 		})
@@ -418,7 +418,7 @@ func TestGZIPChunkTargetSize(t *testing.T) {
 
 	require.NoError(t, chk.Close())
 
-	require.Equal(t, 0, chk.head.size)
+	require.Equal(t, 0, chk.head.UncompressedSize())
 
 	// Even though the seed is static above and results should be deterministic,
 	// we will allow +/- 10% variance
@@ -735,7 +735,7 @@ func BenchmarkHeadBlockIterator(b *testing.B) {
 			h := headBlock{}
 
 			for i := 0; i < j; i++ {
-				if err := h.append(int64(i), "this is the append string"); err != nil {
+				if err := h.Append(int64(i), "this is the append string"); err != nil {
 					b.Fatal(err)
 				}
 			}
@@ -743,7 +743,7 @@ func BenchmarkHeadBlockIterator(b *testing.B) {
 			b.ResetTimer()
 
 			for n := 0; n < b.N; n++ {
-				iter := h.iterator(context.Background(), logproto.BACKWARD, 0, math.MaxInt64, noopStreamPipeline)
+				iter := h.Iterator(context.Background(), logproto.BACKWARD, 0, math.MaxInt64, noopStreamPipeline)
 
 				for iter.Next() {
 					_ = iter.Entry()
@@ -759,7 +759,7 @@ func BenchmarkHeadBlockSampleIterator(b *testing.B) {
 			h := headBlock{}
 
 			for i := 0; i < j; i++ {
-				if err := h.append(int64(i), "this is the append string"); err != nil {
+				if err := h.Append(int64(i), "this is the append string"); err != nil {
 					b.Fatal(err)
 				}
 			}
@@ -767,7 +767,7 @@ func BenchmarkHeadBlockSampleIterator(b *testing.B) {
 			b.ResetTimer()
 
 			for n := 0; n < b.N; n++ {
-				iter := h.sampleIterator(context.Background(), 0, math.MaxInt64, countExtractor)
+				iter := h.SampleIterator(context.Background(), 0, math.MaxInt64, countExtractor)
 
 				for iter.Next() {
 					_ = iter.Sample()
@@ -896,11 +896,11 @@ func TestHeadBlockCheckpointing(t *testing.T) {
 	// ensure blocks are not cut
 	require.Equal(t, 0, len(c.blocks))
 
-	b, err := c.head.CheckpointBytes(c.format, nil)
+	b, err := c.head.CheckpointBytes(nil)
 	require.Nil(t, err)
 
 	hb := &headBlock{}
-	require.Nil(t, hb.FromCheckpoint(b))
+	require.Nil(t, hb.LoadBytes(b))
 	require.Equal(t, c.head, hb)
 }
 
diff --git a/pkg/chunkenc/unordered.go b/pkg/chunkenc/unordered.go
index eed63763517c..924ca0ace93a 100644
--- a/pkg/chunkenc/unordered.go
+++ b/pkg/chunkenc/unordered.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/binary"
+	"fmt"
 	"io"
 	"math"
 	"time"
@@ -21,6 +22,35 @@ import (
 
 var noopStreamPipeline = log.NewNoopPipeline().ForStream(labels.Labels{})
 
+type HeadBlock interface {
+	IsEmpty() bool
+	CheckpointTo(w io.Writer) error
+	CheckpointBytes(b []byte) ([]byte, error)
+	CheckpointSize() int
+	LoadBytes(b []byte) error
+	Serialise(pool WriterPool) ([]byte, error)
+	Reset()
+	Bounds() (mint, maxt int64)
+	Entries() int
+	UncompressedSize() int
+	Convert(HeadBlockFmt) (HeadBlock, error)
+	Append(int64, string) error
+	Iterator(
+		ctx context.Context,
+		direction logproto.Direction,
+		mint,
+		maxt int64,
+		pipeline log.StreamPipeline,
+	) iter.EntryIterator
+	SampleIterator(
+		ctx context.Context,
+		mint,
+		maxt int64,
+		extractor log.StreamSampleExtractor,
+	) iter.SampleIterator
+	Format() HeadBlockFmt
+}
+
 type unorderedHeadBlock struct {
 	// Opted for range tree over skiplist for space reduction.
 	// Inserts: O(log(n))
@@ -38,10 +68,29 @@ func newUnorderedHeadBlock() *unorderedHeadBlock {
 	}
 }
 
-func (hb *unorderedHeadBlock) isEmpty() bool {
+func (hb *unorderedHeadBlock) Format() HeadBlockFmt { return UnorderedHeadBlockFmt }
+
+func (hb *unorderedHeadBlock) IsEmpty() bool {
 	return hb.size == 0
 }
 
+func (hb *unorderedHeadBlock) Bounds() (int64, int64) {
+	return hb.mint, hb.maxt
+}
+
+func (hb *unorderedHeadBlock) Entries() int {
+	return hb.lines
+}
+
+func (hb *unorderedHeadBlock) UncompressedSize() int {
+	return hb.size
+}
+
+func (hb *unorderedHeadBlock) Reset() {
+	x := newUnorderedHeadBlock()
+	*hb = *x
+}
+
 // collection of entries belonging to the same nanosecond
 type nsEntries struct {
 	ts      int64
@@ -52,7 +101,7 @@ func (e *nsEntries) ValueAtDimension(_ uint64) int64 {
 	return e.ts
 }
 
-func (hb *unorderedHeadBlock) append(ts int64, line string) {
+func (hb *unorderedHeadBlock) Append(ts int64, line string) error {
 	// This is an allocation hack. The rangetree lib does not
 	// support the ability to pass a "mutate" function during an insert
 	// and instead will displace any existing entry at the specified timestamp.
@@ -83,6 +132,8 @@ func (hb *unorderedHeadBlock) append(ts int64, line string) {
 
 	hb.size += len(line)
 	hb.lines++
+
+	return nil
 }
 
 // Implements rangetree.Interval
@@ -104,7 +155,7 @@ func (hb *unorderedHeadBlock) forEntries(
 	maxt int64,
 	entryFn func(int64, string) error, // returning an error exits early
 ) (err error) {
-	if hb.isEmpty() || (maxt < hb.mint || hb.maxt < mint) {
+	if hb.IsEmpty() || (maxt < hb.mint || hb.maxt < mint) {
 		return
 	}
 
@@ -157,7 +208,7 @@ func (hb *unorderedHeadBlock) forEntries(
 	return nil
 }
 
-func (hb *unorderedHeadBlock) iterator(
+func (hb *unorderedHeadBlock) Iterator(
 	ctx context.Context,
 	direction logproto.Direction,
 	mint,
@@ -210,7 +261,7 @@ func (hb *unorderedHeadBlock) iterator(
 }
 
 // nolint:unused
-func (hb *unorderedHeadBlock) sampleIterator(
+func (hb *unorderedHeadBlock) SampleIterator(
 	ctx context.Context,
 	mint,
 	maxt int64,
@@ -267,7 +318,7 @@ func (hb *unorderedHeadBlock) sampleIterator(
 
 // nolint:unused
 // serialise is used in creating an ordered, compressed block from an unorderedHeadBlock
-func (hb *unorderedHeadBlock) serialise(pool WriterPool) ([]byte, error) {
+func (hb *unorderedHeadBlock) Serialise(pool WriterPool) ([]byte, error) {
 	inBuf := serializeBytesBufferPool.Get().(*bytes.Buffer)
 	defer func() {
 		inBuf.Reset()
@@ -306,8 +357,26 @@ func (hb *unorderedHeadBlock) serialise(pool WriterPool) ([]byte, error) {
 	return outBuf.Bytes(), nil
 }
 
+func (hb *unorderedHeadBlock) Convert(version HeadBlockFmt) (HeadBlock, error) {
+	if version > OrderedHeadBlockFmt {
+		return hb, nil
+	}
+	out := &headBlock{}
+
+	err := hb.forEntries(
+		context.Background(),
+		logproto.FORWARD,
+		0,
+		math.MaxInt64,
+		func(ts int64, line string) error {
+			return out.Append(ts, line)
+		},
+	)
+	return out, err
+}
+
 // CheckpointSize returns the estimated size of the headblock checkpoint.
-func (hb *unorderedHeadBlock) CheckpointSize(version byte) int {
+func (hb *unorderedHeadBlock) CheckpointSize() int {
 	size := 1                                                          // version
 	size += binary.MaxVarintLen32 * 2                                  // total entries + total size
 	size += binary.MaxVarintLen64 * 2                                  // mint,maxt
@@ -319,20 +388,20 @@ func (hb *unorderedHeadBlock) CheckpointSize(version byte) int {
 // CheckpointBytes serializes a headblock to []byte. This is used by the WAL checkpointing,
 // which does not want to mutate a chunk by cutting it (otherwise risking content address changes), but
 // needs to serialize/deserialize the data to disk to ensure data durability.
-func (hb *unorderedHeadBlock) CheckpointBytes(version byte, b []byte) ([]byte, error) {
+func (hb *unorderedHeadBlock) CheckpointBytes(b []byte) ([]byte, error) {
 	buf := bytes.NewBuffer(b[:0])
-	err := hb.CheckpointTo(version, buf)
+	err := hb.CheckpointTo(buf)
 	return buf.Bytes(), err
 }
 
 // CheckpointTo serializes a headblock to a `io.Writer`. see `CheckpointBytes`.
-func (hb *unorderedHeadBlock) CheckpointTo(version byte, w io.Writer) error {
+func (hb *unorderedHeadBlock) CheckpointTo(w io.Writer) error {
 	eb := EncodeBufferPool.Get().(*encbuf)
 	defer EncodeBufferPool.Put(eb)
 
 	eb.reset()
 
-	eb.putByte(version)
+	eb.putByte(byte(hb.Format()))
 	_, err := w.Write(eb.get())
 	if err != nil {
 		return errors.Wrap(err, "write headBlock version")
@@ -372,7 +441,7 @@ func (hb *unorderedHeadBlock) CheckpointTo(version byte, w io.Writer) error {
 	return nil
 }
 
-func (hb *unorderedHeadBlock) FromCheckpoint(b []byte) error {
+func (hb *unorderedHeadBlock) LoadBytes(b []byte) error {
 	// ensure it's empty
 	*hb = *newUnorderedHeadBlock()
 
@@ -387,9 +456,9 @@ func (hb *unorderedHeadBlock) FromCheckpoint(b []byte) error {
 		return errors.Wrap(db.err(), "verifying headblock header")
 	}
 	switch version {
-	case chunkFormatV1, chunkFormatV2, chunkFormatV3:
+	case UnorderedHeadBlockFmt.Byte():
 	default:
-		return errors.Errorf("incompatible headBlock version (%v), only V1,V2,V3 is currently supported", version)
+		return errors.Errorf("incompatible headBlock version (%v), only V4 is currently supported", version)
 	}
 
 	n := db.uvarint()
@@ -402,7 +471,9 @@ func (hb *unorderedHeadBlock) FromCheckpoint(b []byte) error {
 		ts := db.varint64()
 		lineLn := db.uvarint()
 		line := string(db.bytes(lineLn))
-		hb.append(ts, line)
+		if err := hb.Append(ts, line); err != nil {
+			return err
+		}
 	}
 
 	if err := db.err(); err != nil {
@@ -411,3 +482,36 @@ func (hb *unorderedHeadBlock) FromCheckpoint(b []byte) error {
 
 	return nil
 }
+
+// HeadFromCheckpoint handles reading any head block format and returning the desired form.
+// This is particularly helpful replaying WALs from different configurations
+// such as after enabling unordered writes.
+func HeadFromCheckpoint(b []byte, desired HeadBlockFmt) (HeadBlock, error) {
+	db := decbuf{b: b}
+
+	version := db.byte()
+	if db.err() != nil {
+		return nil, errors.Wrap(db.err(), "verifying headblock header")
+	}
+	format := HeadBlockFmt(version)
+
+	var decodedBlock HeadBlock
+	switch {
+	case format <= OrderedHeadBlockFmt:
+		decodedBlock = &headBlock{}
+	case format == UnorderedHeadBlockFmt:
+		decodedBlock = newUnorderedHeadBlock()
+	default:
+		return nil, fmt.Errorf("unexpected head block version: %v", version)
+	}
+
+	if err := decodedBlock.LoadBytes(b); err != nil {
+		return nil, err
+	}
+
+	if decodedBlock.Format() != desired {
+		return decodedBlock.Convert(desired)
+	}
+	return decodedBlock, nil
+
+}
diff --git a/pkg/chunkenc/unordered_test.go b/pkg/chunkenc/unordered_test.go
index 210c9320851d..a8fe29740ee7 100644
--- a/pkg/chunkenc/unordered_test.go
+++ b/pkg/chunkenc/unordered_test.go
@@ -30,7 +30,7 @@ func iterEq(t *testing.T, exp []entry, got iter.EntryIterator) {
 func Test_forEntriesEarlyReturn(t *testing.T) {
 	hb := newUnorderedHeadBlock()
 	for i := 0; i < 10; i++ {
-		hb.append(int64(i), fmt.Sprint(i))
+		require.Nil(t, hb.Append(int64(i), fmt.Sprint(i)))
 	}
 
 	// forward
@@ -143,10 +143,10 @@ func Test_Unordered_InsertRetrieval(t *testing.T) {
 		t.Run(tc.desc, func(t *testing.T) {
 			hb := newUnorderedHeadBlock()
 			for _, e := range tc.input {
-				hb.append(e.t, e.s)
+				require.Nil(t, hb.Append(e.t, e.s))
 			}
 
-			itr := hb.iterator(
+			itr := hb.Iterator(
 				context.Background(),
 				tc.dir,
 				0,
@@ -205,10 +205,10 @@ func Test_UnorderedBoundedIter(t *testing.T) {
 		t.Run(tc.desc, func(t *testing.T) {
 			hb := newUnorderedHeadBlock()
 			for _, e := range tc.input {
-				hb.append(e.t, e.s)
+				require.Nil(t, hb.Append(e.t, e.s))
 			}
 
-			itr := hb.iterator(
+			itr := hb.Iterator(
 				context.Background(),
 				tc.dir,
 				tc.mint,
@@ -221,26 +221,44 @@ func Test_UnorderedBoundedIter(t *testing.T) {
 	}
 }
 
-func Test_UnorderedHeadBlockCheckpointRoundtrip(t *testing.T) {
-	hb := newUnorderedHeadBlock()
-
+func TestHeadBlockInterop(t *testing.T) {
+	unordered, ordered := newUnorderedHeadBlock(), &headBlock{}
 	for i := 0; i < 100; i++ {
-		hb.append(int64(i), fmt.Sprint(i))
+		require.Nil(t, unordered.Append(int64(99-i), fmt.Sprint(99-i)))
+		require.Nil(t, ordered.Append(int64(i), fmt.Sprint(i)))
 	}
 
 	// turn to bytes
-	b, err := hb.CheckpointBytes(DefaultChunkFormat, nil)
+	b1, err := ordered.CheckpointBytes(nil)
+	require.Nil(t, err)
+	b2, err := unordered.CheckpointBytes(nil)
 	require.Nil(t, err)
 
-	// restore a copy from bytes
-	cpy := newUnorderedHeadBlock()
-	require.Nil(t, cpy.FromCheckpoint(b))
+	// Ensure we can recover ordered checkpoint into ordered headblock
+	recovered, err := HeadFromCheckpoint(b1, OrderedHeadBlockFmt)
+	require.Nil(t, err)
+	require.Equal(t, ordered, recovered)
 
-	// ensure copy's bytes match original
-	cpyBytes, err := cpy.CheckpointBytes(DefaultChunkFormat, nil)
+	// Ensure we can recover ordered checkpoint into unordered headblock
+	recovered, err = HeadFromCheckpoint(b1, UnorderedHeadBlockFmt)
 	require.Nil(t, err)
-	require.Equal(t, b, cpyBytes)
+	require.Equal(t, unordered, recovered)
+
+	// Ensure we can recover unordered checkpoint into ordered headblock
+	recovered, err = HeadFromCheckpoint(b2, OrderedHeadBlockFmt)
+	require.Nil(t, err)
+	require.Equal(t, ordered, recovered)
+
+	// Ensure we can recover unordered checkpoint into unordered headblock
+	recovered, err = HeadFromCheckpoint(b2, UnorderedHeadBlockFmt)
+	require.Nil(t, err)
+	require.Equal(t, unordered, recovered)
+}
 
+// ensure backwards compatibility from when chunk format
+// and head block format was split
+func TestChunkBlockFmt(t *testing.T) {
+	require.Equal(t, chunkFormatV3, byte(OrderedHeadBlockFmt))
 }
 
 func BenchmarkHeadBlockWrites(b *testing.B) {
@@ -254,14 +272,14 @@ func BenchmarkHeadBlockWrites(b *testing.B) {
 	headBlockFn := func() func(int64, string) {
 		hb := &headBlock{}
 		return func(ts int64, line string) {
-			_ = hb.append(ts, line)
+			_ = hb.Append(ts, line)
 		}
 	}
 
 	unorderedHeadBlockFn := func() func(int64, string) {
 		hb := newUnorderedHeadBlock()
 		return func(ts int64, line string) {
-			hb.append(ts, line)
+			_ = hb.Append(ts, line)
 		}
 	}