diff --git a/go.mod b/go.mod
index f47eb26..8f617dc 100644
--- a/go.mod
+++ b/go.mod
@@ -4,12 +4,12 @@ go 1.18
 
 require (
 	github.com/fatih/structtag v1.2.0
-	github.com/google/go-cmp v0.5.5
+	github.com/google/go-cmp v0.6.0
 	github.com/google/gofuzz v1.0.0
 	github.com/unravelin/null v2.1.2+incompatible
 )
 
 require (
 	github.com/mailru/easyjson v0.7.0 // indirect
-	github.com/stretchr/testify v1.6.1 // indirect
+	github.com/stretchr/testify v1.8.2 // indirect
 )
diff --git a/go.sum b/go.sum
index 517f233..237e234 100644
--- a/go.sum
+++ b/go.sum
@@ -1,9 +1,10 @@
-github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/fatih/structtag v1.2.0 h1:/OdNE99OxoI/PqaW/SuSK9uxxT3f/tcSZgon/ssNSx4=
 github.com/fatih/structtag v1.2.0/go.mod h1:mBJUNpUnHmRKrKlQQlmCrh5PuhftFbNv8Ys4/aAZl94=
-github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
-github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/gofuzz v1.0.0 h1:A8PeW59pxE9IoFRqBp37U+mSNaQoZ46F1f0f863XSXw=
 github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
 github.com/mailru/easyjson v0.7.0 h1:aizVhC/NAAcKWb+5QsU1iNOZb4Yws5UO2I+aIprQITM=
@@ -11,12 +12,15 @@ github.com/mailru/easyjson v0.7.0/go.mod h1:KAzv3t3aY1NaHWoQz1+4F1ccyAH66Jk7yos7
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
-github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.2 h1:+h33VjcLVPDHtOdpUCuF+7gSuG3yGIftsP1YvFihtJ8=
+github.com/stretchr/testify v1.8.2/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
 github.com/unravelin/null v2.1.2+incompatible h1:JF+JHiWWs8jDsAAwquTKddV+Rq4moaRzfLzeWW3n1CM=
 github.com/unravelin/null v2.1.2+incompatible/go.mod h1:b0vttVn4a95rTkkj/DT8R6UGjS0Xr+Aw/q7a00kaOM0=
-golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
-golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/null/null.go b/null/null.go
index 9640a60..fe42dc8 100644
--- a/null/null.go
+++ b/null/null.go
@@ -67,6 +67,12 @@ func (c nullIntCodec) New() unsafe.Pointer {
 	return unsafe.Pointer(&null.Int{})
 }
 
+func (c nullIntCodec) Descriptor() plenccodec.Descriptor {
+	d := c.IntCodec.Descriptor()
+	d.ExplicitPresence = true
+	return d
+}
+
 type nullBoolCodec struct {
 	plenccodec.BoolCodec
 }
@@ -101,6 +107,12 @@ func (c nullBoolCodec) New() unsafe.Pointer {
 	return unsafe.Pointer(&null.Bool{})
 }
 
+func (c nullBoolCodec) Descriptor() plenccodec.Descriptor {
+	d := c.BoolCodec.Descriptor()
+	d.ExplicitPresence = true
+	return d
+}
+
 type nullFloatCodec struct {
 	plenccodec.Float64Codec
 }
@@ -136,6 +148,12 @@ func (c nullFloatCodec) New() unsafe.Pointer {
 	return unsafe.Pointer(&null.Float{})
 }
 
+func (c nullFloatCodec) Descriptor() plenccodec.Descriptor {
+	d := c.Float64Codec.Descriptor()
+	d.ExplicitPresence = true
+	return d
+}
+
 type nullStringCodec struct {
 	plenccodec.StringCodec
 }
@@ -169,6 +187,12 @@ func (c nullStringCodec) New() unsafe.Pointer {
 	return unsafe.Pointer(&null.String{})
 }
 
+func (c nullStringCodec) Descriptor() plenccodec.Descriptor {
+	d := c.StringCodec.Descriptor()
+	d.ExplicitPresence = true
+	return d
+}
+
 func (nullStringCodec) WithInterning() plenccodec.Codec {
 	c, _ := plenccodec.StringCodec{}.WithInterning().(*plenccodec.InternedStringCodec)
 	return &internedNullStringCodec{
@@ -225,3 +249,9 @@ func (c *nullTimeCodec) Read(data []byte, ptr unsafe.Pointer, wt plenccore.WireT
 func (c *nullTimeCodec) New() unsafe.Pointer {
 	return unsafe.Pointer(&null.Time{})
 }
+
+func (c nullTimeCodec) Descriptor() plenccodec.Descriptor {
+	d := c.TimeCodec.Descriptor()
+	d.ExplicitPresence = true
+	return d
+}
diff --git a/plenccodec/descriptor.go b/plenccodec/descriptor.go
index 1f98fb4..76377d7 100644
--- a/plenccodec/descriptor.go
+++ b/plenccodec/descriptor.go
@@ -42,12 +42,20 @@ type Descriptor struct {
 	Name string `plenc:"2"`
 	// Type is the type of the field
 	Type FieldType `plenc:"3"`
+	// TypeName is used for struct types and is the name of the struct.
+	TypeName string `plenc:"5"`
 	// Elements is valid for FieldTypeSlice, FieldTypeStruct & FieldTypeMap. For
 	// FieldTypeSlice we expect one entry that describes the elements of the
 	// slice. For FieldTypeStruct we expect an entry for each field in the
 	// struct. For FieldTypeMap we expect two entries. The first is for the key
 	// type and the second is for the map type
 	Elements []Descriptor `plenc:"4"`
+
+	// ExplicitPresence is set if the field has a mechanism to distinguish when
+	// it is not present. So either a pointer type or something from the null
+	// package. If this is not set then a missing value indicates the zero
+	// value, not a null or nil entry.
+	ExplicitPresence bool `plenc:"6"`
 }
 
 func (d *Descriptor) Read(out Outputter, data []byte) (err error) {
diff --git a/plenccodec/map.go b/plenccodec/map.go
index e78ada5..699a267 100644
--- a/plenccodec/map.go
+++ b/plenccodec/map.go
@@ -267,11 +267,20 @@ func (c *MapCodec) Descriptor() Descriptor {
 	vDesc.Index = 2
 	vDesc.Name = "value"
 
+	kTypeName, vTypeName := kDesc.TypeName, vDesc.TypeName
+	if kTypeName == "" {
+		kTypeName = kDesc.Type.String()
+	}
+	if vTypeName == "" {
+		vTypeName = vDesc.Type.String()
+	}
+
 	return Descriptor{
 		Type: FieldTypeSlice,
 		Elements: []Descriptor{
 			{
-				Type: FieldTypeStruct,
+				Type:     FieldTypeStruct,
+				TypeName: fmt.Sprintf("map_%s_%s", kTypeName, vTypeName),
 				Elements: []Descriptor{
 					kDesc,
 					vDesc,
diff --git a/plenccodec/struct.go b/plenccodec/struct.go
index 603b382..c658134 100644
--- a/plenccodec/struct.go
+++ b/plenccodec/struct.go
@@ -232,6 +232,7 @@ func (c *StructCodec) WireType() plenccore.WireType {
 func (c *StructCodec) Descriptor() Descriptor {
 	var d Descriptor
 	d.Type = FieldTypeStruct
+	d.TypeName = c.rtype.Name()
 	d.Elements = make([]Descriptor, len(c.fields))
 	for i, f := range c.fields {
 		d.Elements[i] = f.codec.Descriptor()
diff --git a/plenccodec/struct_test.go b/plenccodec/struct_test.go
index c62f7f0..577d157 100644
--- a/plenccodec/struct_test.go
+++ b/plenccodec/struct_test.go
@@ -2,10 +2,12 @@ package plenccodec_test
 
 import (
 	"fmt"
+	"reflect"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/philpearl/plenc"
+	"github.com/philpearl/plenc/plenccodec"
 )
 
 func TestFieldRemoval(t *testing.T) {
@@ -188,3 +190,39 @@ func TestZeroReuse(t *testing.T) {
 		t.Fatal(diff)
 	}
 }
+
+func TestStructDescriptor(t *testing.T) {
+	type s2 struct {
+		A string `plenc:"1"`
+	}
+	type s1 struct {
+		A int `plenc:"1,flat"`
+		B int `plenc:"2"`
+		C s2  `plenc:"3"`
+	}
+
+	c, err := plenc.CodecForType(reflect.TypeOf(s1{}))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if diff := cmp.Diff(plenccodec.Descriptor{
+		TypeName: "s1",
+		Type:     plenccodec.FieldTypeStruct,
+		Elements: []plenccodec.Descriptor{
+			{Index: 1, Name: "A", Type: plenccodec.FieldTypeFlatInt},
+			{Index: 2, Name: "B", Type: plenccodec.FieldTypeInt},
+			{
+				Index:    3,
+				Name:     "C",
+				Type:     plenccodec.FieldTypeStruct,
+				TypeName: "s2",
+				Elements: []plenccodec.Descriptor{
+					{Index: 1, Name: "A", Type: plenccodec.FieldTypeString},
+				},
+			},
+		},
+	}, c.Descriptor()); diff != "" {
+		t.Fatal(diff)
+	}
+}
diff --git a/plenccodec/wrapper.go b/plenccodec/wrapper.go
index 7e5d2e8..f2c094a 100644
--- a/plenccodec/wrapper.go
+++ b/plenccodec/wrapper.go
@@ -36,7 +36,9 @@ func (p PointerWrapper) WireType() plenccore.WireType {
 }
 
 func (p PointerWrapper) Descriptor() Descriptor {
-	return p.Underlying.Descriptor()
+	d := p.Underlying.Descriptor()
+	d.ExplicitPresence = true
+	return d
 }
 
 func (p PointerWrapper) Size(ptr unsafe.Pointer, tag []byte) int {