diff --git a/tsdb/db_test.go b/tsdb/db_test.go
index 904fdeffc..6d266e872 100644
--- a/tsdb/db_test.go
+++ b/tsdb/db_test.go
@@ -5042,10 +5042,16 @@ func Test_Querier_OOOQuery(t *testing.T) {
 	series1 := labels.FromStrings("foo", "bar1")
 
 	minutes := func(m int64) int64 { return m * time.Minute.Milliseconds() }
-	addSample := func(db *DB, fromMins, toMins, queryMinT, queryMaxT int64, expSamples []chunks.Sample) ([]chunks.Sample, int) {
+	addSample := func(db *DB, fromMins, toMins, queryMinT, queryMaxT int64, expSamples []chunks.Sample, filter func(int64) bool) ([]chunks.Sample, int) {
+		if filter == nil {
+			filter = func(int64) bool { return true }
+		}
 		app := db.Appender(context.Background())
 		totalAppended := 0
 		for m := fromMins; m <= toMins; m += time.Minute.Milliseconds() {
+			if !filter(m / time.Minute.Milliseconds()) {
+				continue
+			}
 			_, err := app.Append(0, series1, m, float64(m))
 			if m >= queryMinT && m <= queryMaxT {
 				expSamples = append(expSamples, sample{t: m, f: float64(m)})
@@ -5084,6 +5090,15 @@ func Test_Querier_OOOQuery(t *testing.T) {
 			oooMinT:     minutes(0),
 			oooMaxT:     minutes(99),
 		},
+		{
+			name:        "query overlapping inorder and ooo samples returns all ingested samples",
+			queryMinT:   minutes(0),
+			queryMaxT:   minutes(200),
+			inOrderMinT: minutes(100),
+			inOrderMaxT: minutes(200),
+			oooMinT:     minutes(180 - opts.OutOfOrderCapMax/2), // Make sure to fit into the OOO head.
+			oooMaxT:     minutes(180),
+		},
 	}
 	for _, tc := range tests {
 		t.Run(fmt.Sprintf("name=%s", tc.name), func(t *testing.T) {
@@ -5093,13 +5108,20 @@ func Test_Querier_OOOQuery(t *testing.T) {
 				require.NoError(t, db.Close())
 			}()
 
-			var expSamples []chunks.Sample
+			var (
+				expSamples []chunks.Sample
+				inoSamples int
+			)
 
-			// Add in-order samples.
-			expSamples, _ = addSample(db, tc.inOrderMinT, tc.inOrderMaxT, tc.queryMinT, tc.queryMaxT, expSamples)
+			// Add in-order samples (at even minutes).
+			expSamples, inoSamples = addSample(db, tc.inOrderMinT, tc.inOrderMaxT, tc.queryMinT, tc.queryMaxT, expSamples, func(t int64) bool { return t%2 == 0 })
+			// Sanity check that filter is not too zealous.
+			require.Positive(t, inoSamples, 0)
 
-			// Add out-of-order samples.
-			expSamples, oooSamples := addSample(db, tc.oooMinT, tc.oooMaxT, tc.queryMinT, tc.queryMaxT, expSamples)
+			// Add out-of-order samples (at odd minutes).
+			expSamples, oooSamples := addSample(db, tc.oooMinT, tc.oooMaxT, tc.queryMinT, tc.queryMaxT, expSamples, func(t int64) bool { return t%2 == 1 })
+			// Sanity check that filter is not too zealous.
+			require.Positive(t, oooSamples, 0)
 
 			sort.Slice(expSamples, func(i, j int) bool {
 				return expSamples[i].T() < expSamples[j].T()
diff --git a/tsdb/head_read.go b/tsdb/head_read.go
index 47f12df99..5e3a76273 100644
--- a/tsdb/head_read.go
+++ b/tsdb/head_read.go
@@ -481,31 +481,12 @@ func (s *memSeries) chunk(id chunks.HeadChunkID, chunkDiskMapper *chunks.ChunkDi
 	return elem, true, offset == 0, nil
 }
 
-// mergedChunks return an iterable over one or more OOO chunks for the given
-// chunks.Meta reference from memory or by m-mapping it from the disk. The
-// returned iterable will be a merge of all the overlapping chunks, if any,
-// amongst all the chunks in the OOOHead.
+// mergedChunks return an iterable over all chunks that overlap the
+// time window [mint,maxt], plus meta.Chunk if populated.
 // If hr is non-nil then in-order chunks are included.
 // This function is not thread safe unless the caller holds a lock.
 // The caller must ensure that s.ooo is not nil.
 func (s *memSeries) mergedChunks(meta chunks.Meta, cdm *chunks.ChunkDiskMapper, hr *headChunkReader, mint, maxt int64, maxMmapRef chunks.ChunkDiskMapperRef) (chunkenc.Iterable, error) {
-	_, cid, _ := unpackHeadChunkRef(meta.Ref)
-
-	// ix represents the index of chunk in the s.mmappedChunks slice. The chunk meta's are
-	// incremented by 1 when new chunk is created, hence (meta - firstChunkID) gives the slice index.
-	// The max index for the s.mmappedChunks slice can be len(s.mmappedChunks)-1, hence if the ix
-	// is len(s.mmappedChunks), it represents the next chunk, which is the head chunk.
-	ix := int(cid) - int(s.ooo.firstOOOChunkID)
-	if ix < 0 || ix > len(s.ooo.oooMmappedChunks) {
-		return nil, storage.ErrNotFound
-	}
-
-	if ix == len(s.ooo.oooMmappedChunks) {
-		if s.ooo.oooHeadChunk == nil {
-			return nil, errors.New("invalid ooo head chunk")
-		}
-	}
-
 	// We create a temporary slice of chunk metas to hold the information of all
 	// possible chunks that may overlap with the requested chunk.
 	tmpChks := make([]chunkMetaAndChunkDiskMapperRef, 0, len(s.ooo.oooMmappedChunks)+1)
diff --git a/tsdb/ooo_head_read.go b/tsdb/ooo_head_read.go
index 55e241fd9..cc98df472 100644
--- a/tsdb/ooo_head_read.go
+++ b/tsdb/ooo_head_read.go
@@ -242,7 +242,7 @@ func NewHeadAndOOOChunkReader(head *Head, mint, maxt int64, cr *headChunkReader,
 
 func (cr *HeadAndOOOChunkReader) ChunkOrIterable(meta chunks.Meta) (chunkenc.Chunk, chunkenc.Iterable, error) {
 	sid, _, isOOO := unpackHeadChunkRef(meta.Ref)
-	if !isOOO {
+	if !isOOO && meta.Chunk == nil { // meta.Chunk can have a copy of OOO head samples, even on non-OOO chunk ID.
 		return cr.cr.ChunkOrIterable(meta)
 	}
 
@@ -253,6 +253,10 @@ func (cr *HeadAndOOOChunkReader) ChunkOrIterable(meta chunks.Meta) (chunkenc.Chu
 	}
 
 	s.Lock()
+	if s.ooo == nil { // Must have s.ooo non-nil to call mergedChunks().
+		s.Unlock()
+		return cr.cr.ChunkOrIterable(meta)
+	}
 	mc, err := s.mergedChunks(meta, cr.head.chunkDiskMapper, cr.cr, cr.mint, cr.maxt, cr.maxMmapRef)
 	s.Unlock()