diff --git a/head.go b/head.go
index e58f629b7..81b2b0ef4 100644
--- a/head.go
+++ b/head.go
@@ -34,7 +34,7 @@ type HeadBlock struct {
 
 	wal *WAL
 
-	bstats BlockStats
+	bstats *BlockStats
 }
 
 // OpenHeadBlock creates a new empty head block.
@@ -53,9 +53,10 @@ func OpenHeadBlock(dir string, l log.Logger) (*HeadBlock, error) {
 		wal:      wal,
 		mapper:   newPositionMapper(nil),
 	}
-
-	b.bstats.MinTime = math.MaxInt64
-	b.bstats.MaxTime = math.MinInt64
+	b.bstats = &BlockStats{
+		MinTime: math.MaxInt64,
+		MaxTime: math.MinInt64,
+	}
 
 	err = wal.ReadAll(&walHandler{
 		series: func(lset labels.Labels) {
@@ -97,7 +98,7 @@ func (h *HeadBlock) dir() string          { return h.d }
 func (h *HeadBlock) persisted() bool      { return false }
 func (h *HeadBlock) index() IndexReader   { return h }
 func (h *HeadBlock) series() SeriesReader { return h }
-func (h *HeadBlock) stats() BlockStats    { return h.bstats }
+func (h *HeadBlock) stats() BlockStats    { return *h.bstats }
 
 // Chunk returns the chunk for the reference number.
 func (h *HeadBlock) Chunk(ref uint32) (chunks.Chunk, error) {
@@ -111,18 +112,12 @@ func (h *HeadBlock) Chunk(ref uint32) (chunks.Chunk, error) {
 }
 
 func (h *HeadBlock) interval() (int64, int64) {
-	h.mtx.RLock()
-	defer h.mtx.RUnlock()
-
 	return h.bstats.MinTime, h.bstats.MaxTime
 }
 
 // Stats returns statisitics about the indexed data.
 func (h *HeadBlock) Stats() (BlockStats, error) {
-	h.mtx.RLock()
-	defer h.mtx.RUnlock()
-
-	return h.bstats, nil
+	return *h.bstats, nil
 }
 
 // LabelValues returns the possible label values
@@ -227,8 +222,8 @@ func (h *HeadBlock) create(hash uint64, lset labels.Labels) *chunkDesc {
 	h.postings.add(cd.ref, term{})
 
 	// For the head block there's exactly one chunk per series.
-	h.bstats.ChunkCount++
-	h.bstats.SeriesCount++
+	atomic.AddUint32(&h.bstats.ChunkCount, 1)
+	atomic.AddUint32(&h.bstats.SeriesCount, 1)
 
 	return cd
 }
@@ -253,6 +248,7 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 		uniqueHashes = map[uint64]uint32{}
 	)
 	h.mtx.RLock()
+	defer h.mtx.RUnlock()
 
 	for i := range samples {
 		s := &samples[i]
@@ -286,8 +282,6 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 		newSamples = append(newSamples, s)
 	}
 
-	h.mtx.RUnlock()
-
 	// Write all new series and samples to the WAL and add it to the
 	// in-mem database on success.
 	if err := h.wal.Log(newSeries, samples); err != nil {
@@ -297,6 +291,7 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 	// After the samples were successfully written to the WAL, there may
 	// be no further failures.
 	if len(newSeries) > 0 {
+		h.mtx.RUnlock()
 		h.mtx.Lock()
 
 		base := len(h.descs)
@@ -309,9 +304,7 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 		}
 
 		h.mtx.Unlock()
-
 		h.mtx.RLock()
-		defer h.mtx.RUnlock()
 	}
 
 	total := len(samples)
@@ -325,20 +318,14 @@ func (h *HeadBlock) appendBatch(samples []hashedSample) error {
 		}
 		cd.append(s.t, s.v)
 
-		if t := h.bstats.MaxTime; s.t > t {
-			// h.bstats.MaxTime = s.t
-			for !atomic.CompareAndSwapInt64(&h.bstats.MaxTime, t, s.t) {
-				if t = h.bstats.MaxTime; s.t <= t {
-					break
-				}
+		for t := h.bstats.MaxTime; s.t > t; t = h.bstats.MaxTime {
+			if atomic.CompareAndSwapInt64(&h.bstats.MaxTime, t, s.t) {
+				break
 			}
 		}
-		if t := h.bstats.MinTime; s.t < t {
-			// h.bstats.MinTime = s.t
-			for !atomic.CompareAndSwapInt64(&h.bstats.MinTime, t, s.t) {
-				if t = h.bstats.MinTime; s.t >= t {
-					break
-				}
+		for t := h.bstats.MinTime; s.t < t; t = h.bstats.MinTime {
+			if atomic.CompareAndSwapInt64(&h.bstats.MinTime, t, s.t) {
+				break
 			}
 		}
 	}