diff --git a/common/net/port.go b/common/net/port.go
index 1e665550a..97c3b1126 100644
--- a/common/net/port.go
+++ b/common/net/port.go
@@ -1,15 +1,38 @@
 package net
 
 import (
+	"errors"
+	"strconv"
+
 	"github.com/v2ray/v2ray-core/common/serial"
 )
 
+var (
+	// ErrorInvalidPortRage indicates an error during port range parsing.
+	ErrorInvalidPortRange = errors.New("Invalid port range.")
+)
+
 type Port serial.Uint16Literal
 
 func PortFromBytes(port []byte) Port {
 	return Port(serial.BytesLiteral(port).Uint16Value())
 }
 
+func PortFromInt(v int) (Port, error) {
+	if v <= 0 || v > 65535 {
+		return Port(0), ErrorInvalidPortRange
+	}
+	return Port(v), nil
+}
+
+func PortFromString(s string) (Port, error) {
+	v, err := strconv.Atoi(s)
+	if err != nil {
+		return Port(0), ErrorInvalidPortRange
+	}
+	return PortFromInt(v)
+}
+
 func (this Port) Value() uint16 {
 	return uint16(this)
 }
diff --git a/common/net/port_json.go b/common/net/port_json.go
index c2458e271..51137a038 100644
--- a/common/net/port_json.go
+++ b/common/net/port_json.go
@@ -4,66 +4,66 @@ package net
 
 import (
 	"encoding/json"
-	"errors"
-	"strconv"
 	"strings"
 
 	"github.com/v2ray/v2ray-core/common/log"
-	"github.com/v2ray/v2ray-core/common/serial"
 )
 
-var (
-	ErrorInvalidPortRange = errors.New("Invalid port range.")
-)
+func parseIntPort(data []byte) (Port, error) {
+	var intPort int
+	err := json.Unmarshal(data, &intPort)
+	if err != nil {
+		return Port(0), err
+	}
+	return PortFromInt(intPort)
+}
 
+func parseStringPort(data []byte) (Port, Port, error) {
+	var s string
+	err := json.Unmarshal(data, &s)
+	if err != nil {
+		return Port(0), Port(0), err
+	}
+	pair := strings.SplitN(s, "-", 2)
+	if len(pair) == 0 {
+		return Port(0), Port(0), ErrorInvalidPortRange
+	}
+	if len(pair) == 1 {
+		port, err := PortFromString(pair[0])
+		return port, port, err
+	}
+
+	fromPort, err := PortFromString(pair[0])
+	if err != nil {
+		return Port(0), Port(0), err
+	}
+	toPort, err := PortFromString(pair[1])
+	if err != nil {
+		return Port(0), Port(0), err
+	}
+	return fromPort, toPort, nil
+}
+
+// UnmarshalJSON implements encoding/json.Unmarshaler.UnmarshalJSON
 func (this *PortRange) UnmarshalJSON(data []byte) error {
-	var maybeint int
-	err := json.Unmarshal(data, &maybeint)
+	port, err := parseIntPort(data)
 	if err == nil {
-		if maybeint <= 0 || maybeint >= 65535 {
-			log.Error("Invalid port [", serial.BytesLiteral(data), "]")
-			return ErrorInvalidPortRange
-		}
-		this.From = Port(maybeint)
-		this.To = Port(maybeint)
+		this.From = port
+		this.To = port
 		return nil
 	}
 
-	var maybestring string
-	err = json.Unmarshal(data, &maybestring)
+	from, to, err := parseStringPort(data)
 	if err == nil {
-		pair := strings.SplitN(maybestring, "-", 2)
-		if len(pair) == 1 {
-			value, err := strconv.Atoi(pair[0])
-			if err != nil || value <= 0 || value >= 65535 {
-				log.Error("Invalid from port ", pair[0])
-				return ErrorInvalidPortRange
-			}
-			this.From = Port(value)
-			this.To = Port(value)
-			return nil
-		} else if len(pair) == 2 {
-			from, err := strconv.Atoi(pair[0])
-			if err != nil || from <= 0 || from >= 65535 {
-				log.Error("Invalid from port ", pair[0])
-				return ErrorInvalidPortRange
-			}
-			this.From = Port(from)
-
-			to, err := strconv.Atoi(pair[1])
-			if err != nil || to <= 0 || to >= 65535 {
-				log.Error("Invalid to port ", pair[1])
-				return ErrorInvalidPortRange
-			}
-			this.To = Port(to)
-
-			if this.From > this.To {
-				log.Error("Invalid port range ", this.From, " -> ", this.To)
-				return ErrorInvalidPortRange
-			}
-			return nil
+		this.From = from
+		this.To = to
+		if this.From > this.To {
+			log.Error("Invalid port range ", this.From, " -> ", this.To)
+			return ErrorInvalidPortRange
 		}
+		return nil
 	}
 
+	log.Error("Invalid port range: ", string(data))
 	return ErrorInvalidPortRange
 }