diff --git a/generic.go b/generic.go
index 309bc15..63c4644 100644
--- a/generic.go
+++ b/generic.go
@@ -39,16 +39,17 @@ func (s *NullableString) UnmarshalJSON(data []byte) (err error) {
 // StringInt is a JSON string representing an integer.
 type StringInt int
 
-func (i *StringInt) MarshalJSON() ([]byte, error) {
-	s := strconv.Itoa(int(*i))
+func (i *StringInt) String() (s string) {
+	s = strconv.Itoa(int(*i))
 	if len(s) <= 4 {
 		s = strings.Repeat("0", 4-len(s)) + s
 	} else if len(s) < 6 {
 		s = strings.Repeat("0", 6-len(s)) + s
 	}
-	return json.Marshal(s)
+	return
 }
 
+func (i *StringInt) MarshalJSON() ([]byte, error) { return json.Marshal(i.String()) }
 func (i *StringInt) UnmarshalJSON(data []byte) (err error) {
 	var v string
 	err = json.Unmarshal(data, &v)