diff --git a/infra/conf/common.go b/infra/conf/common.go
index fd6e732a..1cda2459 100644
--- a/infra/conf/common.go
+++ b/infra/conf/common.go
@@ -2,6 +2,7 @@ package conf
 
 import (
 	"encoding/json"
+	"fmt"
 	"strconv"
 	"strings"
 
@@ -258,6 +259,18 @@ type Int32Range struct {
 	To    int32
 }
 
+func (v Int32Range) MarshalJSON() ([]byte, error) {
+	return json.Marshal(v.String())
+}
+
+func (v Int32Range) String() string {
+	if v.Left == v.Right {
+		return strconv.Itoa(int(v.Left))
+	} else {
+		return fmt.Sprintf("%d-%d", v.Left, v.Right)
+	}
+}
+
 func (v *Int32Range) UnmarshalJSON(data []byte) error {
 	defer v.ensureOrder()
 	var str string