diff --git a/testing/protocmp/reflect.go b/testing/protocmp/reflect.go
index 5b92cb8..0a5e474 100644
--- a/testing/protocmp/reflect.go
+++ b/testing/protocmp/reflect.go
@@ -68,7 +68,7 @@
 	}
 
 	// Range over populated extension fields.
-	for _, xd := range m[messageTypeKey].(messageType).xds {
+	for _, xd := range m[messageTypeKey].(messageMeta).xds {
 		if m.Has(xd) && !f(xd, m.Get(xd)) {
 			return
 		}
@@ -91,7 +91,7 @@
 			return protoreflect.ValueOfMap(reflectMap{})
 		case fd.Message() != nil:
 			return protoreflect.ValueOfMessage(reflectMessage{
-				messageTypeKey: messageType{md: m.Descriptor()},
+				messageTypeKey: messageMeta{md: fd.Message()},
 			})
 		default:
 			return fd.Default()
diff --git a/testing/protocmp/util.go b/testing/protocmp/util.go
index ac6237e..79f3072 100644
--- a/testing/protocmp/util.go
+++ b/testing/protocmp/util.go
@@ -297,11 +297,11 @@
 		return true // treat missing fields as already filtered
 	}
 	var fd protoreflect.FieldDescriptor
-	switch mt := m[messageTypeKey].(messageType); {
+	switch mm := m[messageTypeKey].(messageMeta); {
 	case protoreflect.Name(k).IsValid():
-		fd = mt.md.Fields().ByTextName(k)
+		fd = mm.md.Fields().ByTextName(k)
 	default:
-		fd = mt.xds[k]
+		fd = mm.xds[k]
 	}
 	if fd != nil {
 		return f.names[fd.FullName()]
@@ -376,11 +376,11 @@
 	}
 
 	var fd protoreflect.FieldDescriptor
-	switch mt := m[messageTypeKey].(messageType); {
+	switch mm := m[messageTypeKey].(messageMeta); {
 	case protoreflect.Name(k).IsValid():
-		fd = mt.md.Fields().ByTextName(k)
+		fd = mm.md.Fields().ByTextName(k)
 	default:
-		fd = mt.xds[k]
+		fd = mm.xds[k]
 	}
 	if fd == nil || !fd.Default().IsValid() {
 		return false
diff --git a/testing/protocmp/xform.go b/testing/protocmp/xform.go
index 5a47d0f..7a32e2d 100644
--- a/testing/protocmp/xform.go
+++ b/testing/protocmp/xform.go
@@ -68,20 +68,28 @@
 }
 
 const (
-	messageTypeKey    = "@type"
+	// messageTypeKey indicates the protobuf message type.
+	// The value type is always messageMeta.
+	// From the public API, it presents itself as only the type, but the
+	// underlying data structure holds arbitrary metadata about the message.
+	messageTypeKey = "@type"
+
+	// messageInvalidKey indicates that the message is invalid.
+	// The value is always the boolean "true".
 	messageInvalidKey = "@invalid"
 )
 
-type messageType struct {
+type messageMeta struct {
+	m   proto.Message
 	md  protoreflect.MessageDescriptor
 	xds map[string]protoreflect.ExtensionDescriptor
 }
 
-func (t messageType) String() string {
+func (t messageMeta) String() string {
 	return string(t.md.FullName())
 }
 
-func (t1 messageType) Equal(t2 messageType) bool {
+func (t1 messageMeta) Equal(t2 messageMeta) bool {
 	return t1.md.FullName() == t2.md.FullName()
 }
 
@@ -109,11 +117,18 @@
 // Message values must not be created by or mutated by users.
 type Message map[string]interface{}
 
+// Unwrap returns the original message value.
+// It returns nil if this Message was not constructed from another message.
+func (m Message) Unwrap() proto.Message {
+	mm, _ := m[messageTypeKey].(messageMeta)
+	return mm.m
+}
+
 // Descriptor return the message descriptor.
 // It returns nil for a zero Message value.
 func (m Message) Descriptor() protoreflect.MessageDescriptor {
-	mt, _ := m[messageTypeKey].(messageType)
-	return mt.md
+	mm, _ := m[messageTypeKey].(messageMeta)
+	return mm.md
 }
 
 // ProtoReflect returns a reflective view of m.
@@ -201,7 +216,7 @@
 		case m == nil:
 			return nil
 		case !m.IsValid():
-			return Message{messageTypeKey: messageType{md: m.Descriptor()}, messageInvalidKey: true}
+			return Message{messageTypeKey: messageMeta{m: m.Interface(), md: m.Descriptor()}, messageInvalidKey: true}
 		default:
 			return transformMessage(m)
 		}
@@ -218,7 +233,7 @@
 
 func transformMessage(m protoreflect.Message) Message {
 	mx := Message{}
-	mt := messageType{md: m.Descriptor(), xds: make(map[string]protoreflect.FieldDescriptor)}
+	mt := messageMeta{m: m.Interface(), md: m.Descriptor(), xds: make(map[string]protoreflect.FieldDescriptor)}
 
 	// Handle known and extension fields.
 	m.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
diff --git a/testing/protocmp/xform_test.go b/testing/protocmp/xform_test.go
index c6355d7..a0f7e24 100644
--- a/testing/protocmp/xform_test.go
+++ b/testing/protocmp/xform_test.go
@@ -40,7 +40,7 @@
 			OptionalNestedMessage: &testpb.TestAllTypes_NestedMessage{A: proto.Int32(5)},
 		},
 		want: Message{
-			messageTypeKey:            messageTypeOf(&testpb.TestAllTypes{}),
+			messageTypeKey:            messageMetaOf(&testpb.TestAllTypes{}),
 			"optional_bool":           bool(false),
 			"optional_int32":          int32(-32),
 			"optional_int64":          int64(-64),
@@ -51,7 +51,7 @@
 			"optional_string":         string("string"),
 			"optional_bytes":          []byte("bytes"),
 			"optional_nested_enum":    enumOf(testpb.TestAllTypes_NEG),
-			"optional_nested_message": Message{messageTypeKey: messageTypeOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(5)},
+			"optional_nested_message": Message{messageTypeKey: messageMetaOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(5)},
 		},
 	}, {
 		in: &testpb.TestAllTypes{
@@ -74,7 +74,7 @@
 			},
 		},
 		want: Message{
-			messageTypeKey:    messageTypeOf(&testpb.TestAllTypes{}),
+			messageTypeKey:    messageMetaOf(&testpb.TestAllTypes{}),
 			"repeated_bool":   []bool{false, true},
 			"repeated_int32":  []int32{32, -32},
 			"repeated_int64":  []int64{64, -64},
@@ -89,8 +89,8 @@
 				enumOf(testpb.TestAllTypes_BAR),
 			},
 			"repeated_nested_message": []Message{
-				{messageTypeKey: messageTypeOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(5)},
-				{messageTypeKey: messageTypeOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(-5)},
+				{messageTypeKey: messageMetaOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(5)},
+				{messageTypeKey: messageMetaOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(-5)},
 			},
 		},
 	}, {
@@ -112,7 +112,7 @@
 			},
 		},
 		want: Message{
-			messageTypeKey:      messageTypeOf(&testpb.TestAllTypes{}),
+			messageTypeKey:      messageMetaOf(&testpb.TestAllTypes{}),
 			"map_bool_bool":     map[bool]bool{true: false},
 			"map_int32_int32":   map[int32]int32{-32: 32},
 			"map_int64_int64":   map[int64]int64{-64: 64},
@@ -126,7 +126,7 @@
 				"k": enumOf(testpb.TestAllTypes_FOO),
 			},
 			"map_string_nested_message": map[string]Message{
-				"k": {messageTypeKey: messageTypeOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(5)},
+				"k": {messageTypeKey: messageMetaOf(&testpb.TestAllTypes_NestedMessage{}), "a": int32(5)},
 			},
 		},
 	}, {
@@ -146,7 +146,7 @@
 			return m
 		}(),
 		want: Message{
-			messageTypeKey:                                 messageTypeOf(&testpb.TestAllExtensions{}),
+			messageTypeKey:                                 messageMetaOf(&testpb.TestAllExtensions{}),
 			"[goproto.proto.test.optional_bool]":           bool(false),
 			"[goproto.proto.test.optional_int32]":          int32(-32),
 			"[goproto.proto.test.optional_int64]":          int64(-64),
@@ -157,7 +157,7 @@
 			"[goproto.proto.test.optional_string]":         string("string"),
 			"[goproto.proto.test.optional_bytes]":          []byte("bytes"),
 			"[goproto.proto.test.optional_nested_enum]":    enumOf(testpb.TestAllTypes_NEG),
-			"[goproto.proto.test.optional_nested_message]": Message{messageTypeKey: messageTypeOf(&testpb.TestAllExtensions_NestedMessage{}), "a": int32(5)},
+			"[goproto.proto.test.optional_nested_message]": Message{messageTypeKey: messageMetaOf(&testpb.TestAllExtensions_NestedMessage{}), "a": int32(5)},
 		},
 	}, {
 		in: func() proto.Message {
@@ -182,7 +182,7 @@
 			return m
 		}(),
 		want: Message{
-			messageTypeKey:                         messageTypeOf(&testpb.TestAllExtensions{}),
+			messageTypeKey:                         messageMetaOf(&testpb.TestAllExtensions{}),
 			"[goproto.proto.test.repeated_bool]":   []bool{false, true},
 			"[goproto.proto.test.repeated_int32]":  []int32{32, -32},
 			"[goproto.proto.test.repeated_int64]":  []int64{64, -64},
@@ -197,8 +197,8 @@
 				enumOf(testpb.TestAllTypes_BAR),
 			},
 			"[goproto.proto.test.repeated_nested_message]": []Message{
-				{messageTypeKey: messageTypeOf(&testpb.TestAllExtensions_NestedMessage{}), "a": int32(5)},
-				{messageTypeKey: messageTypeOf(&testpb.TestAllExtensions_NestedMessage{}), "a": int32(-5)},
+				{messageTypeKey: messageMetaOf(&testpb.TestAllExtensions_NestedMessage{}), "a": int32(5)},
+				{messageTypeKey: messageMetaOf(&testpb.TestAllExtensions_NestedMessage{}), "a": int32(-5)},
 			},
 		},
 	}, {
@@ -229,7 +229,7 @@
 			return m
 		}(),
 		want: Message{
-			messageTypeKey: messageTypeOf(&testpb.TestAllTypes{}),
+			messageTypeKey: messageMetaOf(&testpb.TestAllTypes{}),
 			"50000":        protoreflect.RawFields(protopack.Message{protopack.Tag{Number: 50000, Type: protopack.VarintType}, protopack.Uvarint(100)}.Marshal()),
 			"50001":        protoreflect.RawFields(protopack.Message{protopack.Tag{Number: 50001, Type: protopack.Fixed32Type}, protopack.Uint32(200)}.Marshal()),
 			"50002":        protoreflect.RawFields(protopack.Message{protopack.Tag{Number: 50002, Type: protopack.Fixed64Type}, protopack.Uint64(300)}.Marshal()),
@@ -258,6 +258,9 @@
 			if diff := cmp.Diff(tt.want, got); diff != "" {
 				t.Errorf("Transform() mismatch (-want +got):\n%v", diff)
 			}
+			if got.Unwrap() != tt.in {
+				t.Errorf("got.Unwrap() = %p, want %p", got.Unwrap(), tt.in)
+			}
 		})
 	}
 }
@@ -266,6 +269,6 @@
 	return Enum{e.Number(), e.Descriptor()}
 }
 
-func messageTypeOf(m protoreflect.ProtoMessage) messageType {
-	return messageType{md: m.ProtoReflect().Descriptor()}
+func messageMetaOf(m protoreflect.ProtoMessage) messageMeta {
+	return messageMeta{m: m, md: m.ProtoReflect().Descriptor()}
 }