diff --git a/codec_test.go b/codec_test.go
index 4cffe8e..4a8c576 100644
--- a/codec_test.go
+++ b/codec_test.go
@@ -3,8 +3,40 @@ package xml
 import (
 	"bytes"
 	"testing"
+
+	"github.com/unistack-org/micro/v3/codec"
 )
 
+func TestFrame(t *testing.T) {
+	s := &codec.Frame{Data: []byte("test")}
+
+	buf, err := NewCodec().Marshal(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(buf, []byte(`test`)) {
+		t.Fatalf("bytes not equal %s != %s", buf, `test`)
+	}
+}
+
+func TestFrameFlatten(t *testing.T) {
+	s := &struct {
+		One  string
+		Name *codec.Frame `xml:"name" codec:"flatten"`
+	}{
+		One:  "xx",
+		Name: &codec.Frame{Data: []byte("test")},
+	}
+
+	buf, err := NewCodec().Marshal(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(buf, []byte(`test`)) {
+		t.Fatalf("bytes not equal %s != %s", buf, `test`)
+	}
+}
+
 func TestReadBody(t *testing.T) {
 	s := &struct {
 		Name string
diff --git a/xml.go b/xml.go
index dde53fc..4f59702 100644
--- a/xml.go
+++ b/xml.go
@@ -20,22 +20,22 @@ const (
 )
 
 func (c *xmlCodec) Marshal(v interface{}, opts ...codec.Option) ([]byte, error) {
-	switch m := v.(type) {
-	case nil:
+	if v == nil {
 		return nil, nil
-	case *codec.Frame:
-		return m.Data, nil
 	}
 
 	options := c.opts
 	for _, o := range opts {
 		o(&options)
 	}
-
 	if nv, nerr := rutil.StructFieldByTag(v, options.TagName, flattenTag); nerr == nil {
 		v = nv
 	}
 
+	if m, ok := v.(*codec.Frame); ok {
+		return m.Data, nil
+	}
+
 	return xml.Marshal(v)
 }
 
@@ -44,11 +44,6 @@ func (c *xmlCodec) Unmarshal(b []byte, v interface{}, opts ...codec.Option) erro
 		return nil
 	}
 
-	if m, ok := v.(*codec.Frame); ok {
-		m.Data = b
-		return nil
-	}
-
 	options := c.opts
 	for _, o := range opts {
 		o(&options)
@@ -58,6 +53,11 @@ func (c *xmlCodec) Unmarshal(b []byte, v interface{}, opts ...codec.Option) erro
 		v = nv
 	}
 
+	if m, ok := v.(*codec.Frame); ok {
+		m.Data = b
+		return nil
+	}
+
 	return xml.Unmarshal(b, v)
 }