diff --git a/tsdb/head_append.go b/tsdb/head_append.go
index 988ce9397..ea2ee0091 100644
--- a/tsdb/head_append.go
+++ b/tsdb/head_append.go
@@ -1469,13 +1469,13 @@ func (s *memSeries) mmapCurrentOOOHeadChunk(chunkDiskMapper *chunks.ChunkDiskMap
 		handleChunkWriteError(err)
 		return nil
 	}
-	chunkRefs := make([]chunks.ChunkDiskMapperRef, 0, 1)
+	chunkRefs := make([]chunks.ChunkDiskMapperRef, 0, len(chks))
 	for _, memchunk := range chks {
 		if len(s.ooo.oooMmappedChunks) >= (oooChunkIDMask - 1) {
 			level.Error(logger).Log("msg", "Too many OOO chunks, dropping data", "series", s.lset.String())
 			break
 		}
-		chunkRef := chunkDiskMapper.WriteChunk(s.ref, s.ooo.oooHeadChunk.minTime, s.ooo.oooHeadChunk.maxTime, memchunk.chunk, true, handleChunkWriteError)
+		chunkRef := chunkDiskMapper.WriteChunk(s.ref, memchunk.minTime, memchunk.maxTime, memchunk.chunk, true, handleChunkWriteError)
 		chunkRefs = append(chunkRefs, chunkRef)
 		s.ooo.oooMmappedChunks = append(s.ooo.oooMmappedChunks, &mmappedChunk{
 			ref:        chunkRef,
diff --git a/tsdb/ooo_head_read.go b/tsdb/ooo_head_read.go
index 66ae93325..746d38a65 100644
--- a/tsdb/ooo_head_read.go
+++ b/tsdb/ooo_head_read.go
@@ -111,7 +111,7 @@ func getOOOSeriesChunks(s *memSeries, mint, maxt int64, lastGarbageCollectedMmap
 					return nil
 				}
 				for _, chk := range chks {
-					addChunk(c.minTime, c.maxTime, ref, chk.chunk)
+					addChunk(chk.minTime, chk.maxTime, ref, chk.chunk)
 				}
 			} else {
 				var emptyChunk chunkenc.Chunk