diff --git a/subscribe/message.go b/subscribe/message.go
index 86f1d10..5d1a346 100644
--- a/subscribe/message.go
+++ b/subscribe/message.go
@@ -44,15 +44,15 @@ func (st TargetType) String() string {
 	return targetTypeID[st]
 }
 
-func (st TargetType) MarshalJSON() ([]byte, error) {
-	value, ok := targetTypeID[st]
+func (st *TargetType) MarshalJSON() ([]byte, error) {
+	value, ok := targetTypeID[*st]
 	if !ok {
 		return nil, fmt.Errorf("Invalid EnumType[%s] value", st)
 	}
 	return json.Marshal(value)
 }
 
-func (st TargetType) UnmarshalJSON(b []byte) error {
+func (st *TargetType) UnmarshalJSON(b []byte) error {
 	// unmarshal as string
 	var s string
 	err := json.Unmarshal(b, &s)
@@ -64,6 +64,6 @@ func (st TargetType) UnmarshalJSON(b []byte) error {
 	if !ok {
 		return fmt.Errorf("Invalid EnumType[%s] value", s)
 	}
-	st = value
+	st = &value
 	return nil
 }