diff --git a/pkg/histogram/sparse_histogram.go b/pkg/histogram/sparse_histogram.go
index 6ea1cb76e..0e4df9372 100644
--- a/pkg/histogram/sparse_histogram.go
+++ b/pkg/histogram/sparse_histogram.go
@@ -14,7 +14,6 @@
 package histogram
 
 type SparseHistogram struct {
-	Ts                               int64
 	Count, ZeroCount                 uint64
 	Sum, ZeroThreshold               float64
 	Schema                           int32
diff --git a/tsdb/chunkenc/chunk.go b/tsdb/chunkenc/chunk.go
index 0eddb4ea5..63d3a6111 100644
--- a/tsdb/chunkenc/chunk.go
+++ b/tsdb/chunkenc/chunk.go
@@ -73,7 +73,7 @@ type Chunk interface {
 // Appender adds sample pairs to a chunk.
 type Appender interface {
 	Append(int64, float64)
-	AppendHistogram(h histogram.SparseHistogram)
+	AppendHistogram(t int64, h histogram.SparseHistogram)
 }
 
 // Iterator is a simple iterator that can only get the next value.
diff --git a/tsdb/chunkenc/histo.go b/tsdb/chunkenc/histo.go
index d5c6d1afb..08f2070e6 100644
--- a/tsdb/chunkenc/histo.go
+++ b/tsdb/chunkenc/histo.go
@@ -206,9 +206,10 @@ type histoAppender struct {
 	posSpans, negSpans []histogram.Span
 
 	// for the fields that are tracked as dod's
+	// note that we expect to handle negative deltas (e.g. resets) by creating new chunks, we still want to support it in general hence signed integer types
 	t                           int64
 	cnt, zcnt                   uint64
-	tDelta, cntDelta, zcntDelta uint64
+	tDelta, cntDelta, zcntDelta int64
 
 	posbuckets, negbuckets           []int64
 	posbucketsDelta, negbucketsDelta []int64
@@ -260,8 +261,8 @@ func (a *histoAppender) Append(int64, float64) {
 
 // AppendHistogram appends a SparseHistogram to the chunk
 // we assume the histogram is properly structured. E.g. that the number pos/neg buckets used corresponds to the number conveyed by the pos/neg span structures
-func (a *histoAppender) AppendHistogram(h histogram.SparseHistogram) {
-	var tDelta, cntDelta, zcntDelta uint64
+func (a *histoAppender) AppendHistogram(t int64, h histogram.SparseHistogram) {
+	var tDelta, cntDelta, zcntDelta int64
 	num := binary.BigEndian.Uint16(a.b.bytes())
 
 	if num == 0 {
@@ -273,7 +274,7 @@ func (a *histoAppender) AppendHistogram(h histogram.SparseHistogram) {
 		a.schema = h.Schema
 		a.posSpans, a.negSpans = h.PositiveSpans, h.NegativeSpans
 
-		putVarint(a.b, a.buf64, h.Ts)
+		putVarint(a.b, a.buf64, t)
 		putUvarint(a.b, a.buf64, h.Count)
 		putUvarint(a.b, a.buf64, h.ZeroCount)
 		a.b.writeBits(math.Float64bits(h.Sum), 64)
@@ -284,16 +285,13 @@ func (a *histoAppender) AppendHistogram(h histogram.SparseHistogram) {
 			putVarint(a.b, a.buf64, buck)
 		}
 	} else if num == 1 {
-		tDelta = uint64(h.Ts - a.t)
+		tDelta = t - a.t
+		cntDelta = int64(h.Count) - int64(a.cnt)
+		zcntDelta = int64(h.ZeroCount) - int64(a.zcnt)
 
-		// WARNING: we assume all counts go up. what guarantee do we have this is true? uint may underflow if not.
-
-		cntDelta = h.Count - a.cnt
-		zcntDelta = h.ZeroCount - a.zcnt
-
-		putUvarint(a.b, a.buf64, tDelta)
-		putUvarint(a.b, a.buf64, cntDelta)
-		putUvarint(a.b, a.buf64, zcntDelta)
+		putVarint(a.b, a.buf64, tDelta)
+		putVarint(a.b, a.buf64, cntDelta)
+		putVarint(a.b, a.buf64, zcntDelta)
 
 		a.writeSumDelta(h.Sum)
 
@@ -308,13 +306,13 @@ func (a *histoAppender) AppendHistogram(h histogram.SparseHistogram) {
 			a.negbucketsDelta[i] = delta
 		}
 	} else {
-		tDelta = uint64(h.Ts - a.t)
-		cntDelta = h.Count - a.cnt
-		zcntDelta = h.ZeroCount - a.zcnt
+		tDelta = t - a.t
+		cntDelta = int64(h.Count) - int64(a.cnt)
+		zcntDelta = int64(h.ZeroCount) - int64(a.zcnt)
 
-		tDod := int64(tDelta - a.tDelta)
-		cntDod := int64(cntDelta - a.cntDelta)
-		zcntDod := int64(zcntDelta - a.zcntDelta)
+		tDod := tDelta - a.tDelta
+		cntDod := cntDelta - a.cntDelta
+		zcntDod := zcntDelta - a.zcntDelta
 
 		putDod(a.b, tDod)
 		putDod(a.b, cntDod)
@@ -338,7 +336,7 @@ func (a *histoAppender) AppendHistogram(h histogram.SparseHistogram) {
 
 	binary.BigEndian.PutUint16(a.b.bytes(), num+1)
 
-	a.t = h.Ts
+	a.t = t
 	a.cnt = h.Count
 	a.zcnt = h.ZeroCount
 	a.tDelta = tDelta
@@ -399,7 +397,7 @@ type histoIterator struct {
 	// for the fields that are tracked as dod's
 	t                           int64
 	cnt, zcnt                   uint64
-	tDelta, cntDelta, zcntDelta uint64
+	tDelta, cntDelta, zcntDelta int64
 
 	posbuckets, negbuckets           []int64
 	posbucketsDelta, negbucketsDelta []int64
@@ -424,9 +422,8 @@ func (it *histoIterator) Seek(t int64) bool {
 	}
 	return true
 }
-func (it *histoIterator) At() (h histogram.SparseHistogram) {
-	return histogram.SparseHistogram{
-		Ts:              it.t,
+func (it *histoIterator) At() (t int64, h histogram.SparseHistogram) {
+	return it.t, histogram.SparseHistogram{
 		Count:           it.cnt,
 		ZeroCount:       it.zcnt,
 		Sum:             it.sum,
@@ -524,7 +521,7 @@ func (it *histoIterator) Next() bool {
 	}
 
 	if it.numRead == 1 {
-		tDelta, err := binary.ReadUvarint(&it.br)
+		tDelta, err := binary.ReadVarint(&it.br)
 		if err != nil {
 			it.err = err
 			return false
@@ -532,21 +529,21 @@ func (it *histoIterator) Next() bool {
 		it.tDelta = tDelta
 		it.t += int64(it.tDelta)
 
-		cntDelta, err := binary.ReadUvarint(&it.br)
+		cntDelta, err := binary.ReadVarint(&it.br)
 		if err != nil {
 			it.err = err
 			return false
 		}
 		it.cntDelta = cntDelta
-		it.cnt += it.cntDelta
+		it.cnt = uint64(int64(it.cnt) + it.cntDelta)
 
-		zcntDelta, err := binary.ReadUvarint(&it.br)
+		zcntDelta, err := binary.ReadVarint(&it.br)
 		if err != nil {
 			it.err = err
 			return false
 		}
 		it.zcntDelta = zcntDelta
-		it.zcnt += it.zcntDelta
+		it.zcnt = uint64(int64(it.zcnt) + it.zcntDelta)
 
 		ok := it.readSum()
 		if !ok {
@@ -580,22 +577,22 @@ func (it *histoIterator) Next() bool {
 	if !ok {
 		return ok
 	}
-	it.tDelta = uint64(int64(it.tDelta) + tDod)
-	it.t += int64(it.tDelta)
+	it.tDelta = it.tDelta + tDod
+	it.t += it.tDelta
 
 	cntDod, ok := it.readDod()
 	if !ok {
 		return ok
 	}
-	it.cntDelta = uint64(int64(it.cntDelta) + cntDod)
-	it.cnt += it.cntDelta
+	it.cntDelta = it.cntDelta + cntDod
+	it.cnt = uint64(int64(it.cnt) + it.cntDelta)
 
 	zcntDod, ok := it.readDod()
 	if !ok {
 		return ok
 	}
-	it.zcntDelta = uint64(int64(it.zcntDelta) + zcntDod)
-	it.zcnt += it.zcntDelta
+	it.zcntDelta = it.zcntDelta + zcntDod
+	it.zcnt = uint64(int64(it.zcnt) + it.zcntDelta)
 
 	ok = it.readSum()
 	if !ok {
diff --git a/tsdb/chunkenc/histo_test.go b/tsdb/chunkenc/histo_test.go
index c5e3b5b2b..907756a68 100644
--- a/tsdb/chunkenc/histo_test.go
+++ b/tsdb/chunkenc/histo_test.go
@@ -24,12 +24,20 @@ func TestHistoChunkSameBuckets(t *testing.T) {
 
 	c := NewHistoChunk()
 
+	type res struct {
+		t int64
+		h histogram.SparseHistogram
+	}
+
+	// create fresh appender and add the first histogram
+
 	app, err := c.Appender()
 	require.NoError(t, err)
 	require.Equal(t, c.NumSamples(), 0)
 
+	ts := int64(1234567890)
+
 	h := histogram.SparseHistogram{
-		Ts:        1234567890,
 		Count:     5,
 		ZeroCount: 2,
 		Sum:       18.4,
@@ -44,11 +52,11 @@ func TestHistoChunkSameBuckets(t *testing.T) {
 		NegativeBuckets: []int64{},
 	}
 
-	app.AppendHistogram(h)
+	app.AppendHistogram(ts, h)
 	require.Equal(t, c.NumSamples(), 1)
 
-	exp := []histogram.SparseHistogram{
-		h,
+	exp := []res{
+		{t: ts, h: h},
 	}
 
 	// TODO add an update
@@ -66,9 +74,10 @@ func TestHistoChunkSameBuckets(t *testing.T) {
 	// 1. Expand iterator in simple case.
 	it1 := c.iterator(nil)
 	require.NoError(t, it1.Err())
-	var res1 []histogram.SparseHistogram
+	var res1 []res
 	for it1.Next() {
-		res1 = append(res1, it1.At())
+		ts, h := it1.At()
+		res1 = append(res1, res{t: ts, h: h})
 	}
 	require.NoError(t, it1.Err())
 	require.Equal(t, exp, res1)
diff --git a/tsdb/chunkenc/xor.go b/tsdb/chunkenc/xor.go
index b46e88854..d1dc09f8f 100644
--- a/tsdb/chunkenc/xor.go
+++ b/tsdb/chunkenc/xor.go
@@ -149,7 +149,7 @@ type xorAppender struct {
 	trailing uint8
 }
 
-func (a *xorAppender) AppendHistogram(h histogram.SparseHistogram) {
+func (a *xorAppender) AppendHistogram(t int64, h histogram.SparseHistogram) {
 	panic("cannot call xorAppender.AppendHistogram().")
 }
 
diff --git a/tsdb/head.go b/tsdb/head.go
index 296fa56c0..42e4f86f0 100644
--- a/tsdb/head.go
+++ b/tsdb/head.go
@@ -1199,7 +1199,7 @@ func (a *initAppender) AppendHistogram(ref uint64, l labels.Labels, sh histogram
 	if a.app != nil {
 		return a.app.AppendHistogram(ref, l, sh)
 	}
-	a.head.initTime(sh.Ts)
+	//a.head.initTime(sh.Ts) FIXME(ganesh)
 	a.app = a.head.appender()
 
 	return a.app.AppendHistogram(ref, l, sh)