diff --git a/editor.go b/editor.go
index 792a384..be72fd1 100644
--- a/editor.go
+++ b/editor.go
@@ -310,18 +310,16 @@ func passThroughImpl(pp *pc.PointCloud, core func(_, _ *pc.PointCloud) int) (*pc
 }
 
 func (e *editor) merge(pp *pc.PointCloud) error {
-	pcNew := &pc.PointCloud{
-		PointCloudHeader: e.pp.PointCloudHeader.Clone(),
-		Points:           e.pp.Points + pp.Points,
-		Data:             append(e.pp.Data[:e.pp.Stride()*e.pp.Points], pp.Data...),
-	}
-	pcNew.Width = pcNew.Points
-	pcNew.Height = 1
-
-	if err := e.push(newUndoDataEntireCloud(e.pp)); err != nil {
+	if err := e.push(&undoDataSize{
+		Points: e.pp.Points,
+		Width:  e.pp.Width,
+		Height: e.pp.Height,
+	}); err != nil {
 		return err
 	}
-	e.pp = pcNew
+	n := e.pp.Points + pp.Points
+	data := append(e.pp.Data[:e.pp.Stride()*e.pp.Points], pp.Data...)
+	e.pp = newCloudView(e.pp, n, n, 1, data)
 	runtime.GC()
 	return nil
 }
diff --git a/record.go b/record.go
index cf5c040..9ca1c00 100644
--- a/record.go
+++ b/record.go
@@ -21,6 +21,20 @@ type undoData interface {
 func init() {
 	gob.Register(&undoDataEntireCloud{})
 	gob.Register(&undoDataLabels{})
+	gob.Register(&undoDataSize{})
+}
+
+// pcgol caches an unsafe float32 alias of Data keyed only by its base pointer,
+// so a change of the Data length must be delivered in a fresh PointCloud.
+func newCloudView(pp *pc.PointCloud, points, width, height int, data []byte) *pc.PointCloud {
+	out := &pc.PointCloud{
+		PointCloudHeader: pp.PointCloudHeader.Clone(),
+		Points:           points,
+		Data:             data,
+	}
+	out.Width = width
+	out.Height = height
+	return out
 }
 
 var (
@@ -97,6 +111,25 @@ func (p *undoDataLabels) payload() []byte {
 
 func (p *undoDataLabels) setPayload([]byte) {}
 
+type undoDataSize struct {
+	Points, Width, Height int
+}
+
+func (p *undoDataSize) restore(pp *pc.PointCloud) (*pc.PointCloud, error) {
+	stride := pp.Stride()
+	if stride <= 0 || p.Points < 0 || p.Width < 0 || p.Height < 0 ||
+		p.Points > pp.Points || p.Points > len(pp.Data)/stride {
+		return nil, errBrokenRecord
+	}
+	return newCloudView(pp, p.Points, p.Width, p.Height, pp.Data[:p.Points*stride]), nil
+}
+
+func (p *undoDataSize) payload() []byte {
+	return nil
+}
+
+func (p *undoDataSize) setPayload([]byte) {}
+
 // A record is this encoding followed by the raw payload.
 func encodeUndoData(w io.Writer, d undoData) error {
 	return gob.NewEncoder(w).Encode(&d)
diff --git a/record_test.go b/record_test.go
index 2f7c1e0..256b0e3 100644
--- a/record_test.go
+++ b/record_test.go
@@ -74,6 +74,24 @@ func TestUndoDataLabelsRestore(t *testing.T) {
 	assertCloudEqual(t, orig, out)
 }
 
+func TestUndoDataSizeRestore(t *testing.T) {
+	orig := makeTestCloud(t, 100, 10, 10)
+	pp := cloneCloud(orig)
+
+	p := &undoDataSize{Points: pp.Points, Width: pp.Width, Height: pp.Height}
+	added := makeTestCloud(t, 10, 10, 1)
+	pp.Data = append(pp.Data, added.Data...)
+	pp.Points += added.Points
+	pp.Width = pp.Points
+	pp.Height = 1
+
+	out, err := p.restore(pp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertCloudEqual(t, orig, out)
+}
+
 func TestUndoDataEntireCloudRestore(t *testing.T) {
 	orig := makeTestCloud(t, 100, 10, 10)
 	pp := makeTestCloud(t, 5, 5, 1)
@@ -95,6 +113,7 @@ func TestRecordEncodeDecodeRoundTrip(t *testing.T) {
 	for name, d := range map[string]undoData{
 		"EntireCloud": newUndoDataEntireCloud(orig),
 		"Labels":      &undoDataLabels{Indices: []uint32{1, 2, 42}, OldLabels: []uint32{7, 8, 9}},
+		"Size":        &undoDataSize{Points: 90, Width: 9, Height: 10},
 	} {
 		t.Run(name, func(t *testing.T) {
 			var buf bytes.Buffer