diff --git a/tsdb/ooo_head_read.go b/tsdb/ooo_head_read.go
index dd45a9ced1..59e33111e4 100644
--- a/tsdb/ooo_head_read.go
+++ b/tsdb/ooo_head_read.go
@@ -29,8 +29,6 @@ import (
 	"github.com/prometheus/prometheus/tsdb/tombstones"
 )
 
-var _ IndexReader = &OOOHeadIndexReader{}
-
 // OOOHeadIndexReader implements IndexReader so ooo samples in the head can be
 // accessed.
 // It also has a reference to headIndexReader so we can leverage on its
@@ -42,8 +40,6 @@ type OOOHeadIndexReader struct {
 	lastGarbageCollectedMmapRef chunks.ChunkDiskMapperRef
 }
 
-var _ chunkenc.Iterable = &mergedOOOChunks{}
-
 // mergedOOOChunks holds the list of iterables for overlapping chunks.
 type mergedOOOChunks struct {
 	chunkIterables []chunkenc.Iterable
@@ -66,6 +62,53 @@ func (oh *OOOHeadIndexReader) Series(ref storage.SeriesRef, builder *labels.Scra
 	return oh.series(ref, builder, chks, oh.lastGarbageCollectedMmapRef, 0)
 }
 
+type MultiChunk struct {
+	chunks []chunkenc.Chunk
+}
+
+func (c MultiChunk) Iterator(it chunkenc.Iterator) chunkenc.Iterator {
+	switch len(c.chunks) {
+	case 0:
+		return chunkenc.NewNopIterator()
+	case 1:
+		return c.chunks[0].Iterator(it)
+	default:
+		iterators := make([]chunkenc.Iterator, 0, len(c.chunks))
+		for _, chk := range c.chunks {
+			iterators = append(iterators, chk.Iterator(nil))
+		}
+		return storage.ChainSampleIteratorFromIterators(it, iterators)
+	}
+}
+
+func (c MultiChunk) Appender() (chunkenc.Appender, error) {
+	return nil, errors.New("not implemented")
+}
+
+func (c MultiChunk) Bytes() []byte {
+	return nil
+}
+
+func (c MultiChunk) Compact() {
+	// no-op
+}
+
+func (c MultiChunk) Encoding() chunkenc.Encoding {
+	return chunkenc.EncNone
+}
+
+func (c MultiChunk) NumSamples() int {
+	sum := 0
+	for _, chk := range c.chunks {
+		sum += chk.NumSamples()
+	}
+	return sum
+}
+
+func (c MultiChunk) Reset([]byte) {
+	// no-op
+}
+
 // lastGarbageCollectedMmapRef gives the last mmap chunk that may be being garbage collected and so
 // any chunk at or before this ref will not be considered. 0 disables this check.
 //
@@ -109,14 +152,16 @@ func (oh *OOOHeadIndexReader) series(ref storage.SeriesRef, builder *labels.Scra
 		if c.OverlapsClosedInterval(oh.mint, oh.maxt) && maxMmapRef == 0 {
 			ref := chunks.ChunkRef(chunks.NewHeadChunkRef(s.ref, s.oooHeadChunkID(len(s.ooo.oooMmappedChunks))))
 			if len(c.chunk.samples) > 0 { // Empty samples happens in tests, at least.
+				headChunks := MultiChunk{}
 				chks, err := s.ooo.oooHeadChunk.chunk.ToEncodedChunks(c.minTime, c.maxTime)
 				if err != nil {
 					handleChunkWriteError(err)
 					return nil
 				}
 				for _, chk := range chks {
-					addChunk(chk.minTime, chk.maxTime, ref, chk.chunk)
+					headChunks.chunks = append(headChunks.chunks, chk.chunk)
 				}
+				addChunk(c.minTime, c.maxTime, ref, headChunks)
 			} else {
 				var emptyChunk chunkenc.Chunk
 				addChunk(c.minTime, c.maxTime, ref, emptyChunk)
diff --git a/tsdb/ooo_head_read_test.go b/tsdb/ooo_head_read_test.go
index ec73a59f8b..f8ce8ecb82 100644
--- a/tsdb/ooo_head_read_test.go
+++ b/tsdb/ooo_head_read_test.go
@@ -31,6 +31,13 @@ import (
 	"github.com/prometheus/prometheus/tsdb/wlog"
 )
 
+// Type assertions.
+var (
+	_ chunkenc.Chunk    = &MultiChunk{}
+	_ chunkenc.Iterable = &mergedOOOChunks{}
+	_ IndexReader       = &OOOHeadIndexReader{}
+)
+
 type chunkInterval struct {
 	// because we permutate the order of chunks, we cannot determine at test declaration time which chunkRefs we expect in the Output.
 	// This ID matches expected output chunks against test input chunks, the test runner will assert the chunkRef for the matching chunk