diff --git a/common/dice/dice.go b/common/dice/dice.go
new file mode 100644
index 000000000..01d2ca804
--- /dev/null
+++ b/common/dice/dice.go
@@ -0,0 +1,12 @@
+package dice
+
+import (
+	"math/rand"
+)
+
+func Roll(n int) int {
+	if n == 1 {
+		return 0
+	}
+	return rand.Intn(n)
+}
diff --git a/proxy/vmess/outbound/receiver.go b/proxy/vmess/outbound/receiver.go
index 31e20d644..591f08274 100644
--- a/proxy/vmess/outbound/receiver.go
+++ b/proxy/vmess/outbound/receiver.go
@@ -1,10 +1,10 @@
 package outbound
 
 import (
-	"math/rand"
 	"sync"
 	"time"
 
+	"github.com/v2ray/v2ray-core/common/dice"
 	v2net "github.com/v2ray/v2ray-core/common/net"
 	"github.com/v2ray/v2ray-core/proxy/vmess"
 )
@@ -44,12 +44,7 @@ func (this *Receiver) AddUser(user *vmess.User) {
 }
 
 func (this *Receiver) PickUser() *vmess.User {
-	userLen := len(this.Accounts)
-	userIdx := 0
-	if userLen > 1 {
-		userIdx = rand.Intn(userLen)
-	}
-	return this.Accounts[userIdx]
+	return this.Accounts[dice.Roll(len(this.Accounts))]
 }
 
 type ExpiringReceiver struct {
@@ -108,11 +103,7 @@ func (this *ReceiverManager) pickDetour() *Receiver {
 		return nil
 	}
 	this.detourAccess.RLock()
-	idx := 0
-	detourLen := len(this.detours)
-	if detourLen > 1 {
-		idx = rand.Intn(detourLen)
-	}
+	idx := dice.Roll(len(this.detours))
 	rec := this.detours[idx]
 	this.detourAccess.RUnlock()
 
@@ -129,14 +120,7 @@ func (this *ReceiverManager) pickDetour() *Receiver {
 }
 
 func (this *ReceiverManager) pickStdReceiver() *Receiver {
-	receiverLen := len(this.receivers)
-
-	receiverIdx := 0
-	if receiverLen > 1 {
-		receiverIdx = rand.Intn(receiverLen)
-	}
-
-	return this.receivers[receiverIdx]
+	return this.receivers[dice.Roll(len(this.receivers))]
 }
 
 func (this *ReceiverManager) PickReceiver() (v2net.Destination, *vmess.User) {
diff --git a/proxy/vmess/user.go b/proxy/vmess/user.go
index 700670e13..31cd0b6ec 100644
--- a/proxy/vmess/user.go
+++ b/proxy/vmess/user.go
@@ -1,7 +1,7 @@
 package vmess
 
 import (
-	"math/rand"
+	"github.com/v2ray/v2ray-core/common/dice"
 )
 
 type UserLevel byte
@@ -39,11 +39,7 @@ func (this *User) AnyValidID() *ID {
 	if len(this.AlterIDs) == 0 {
 		return this.ID
 	}
-	if len(this.AlterIDs) == 1 {
-		return this.AlterIDs[0]
-	}
-	idx := rand.Intn(len(this.AlterIDs))
-	return this.AlterIDs[idx]
+	return this.AlterIDs[dice.Roll(len(this.AlterIDs))]
 }
 
 type UserSettings struct {
diff --git a/shell/point/inbound_detour_always.go b/shell/point/inbound_detour_always.go
index de95c0e6c..dbcf2f841 100644
--- a/shell/point/inbound_detour_always.go
+++ b/shell/point/inbound_detour_always.go
@@ -1,9 +1,8 @@
 package point
 
 import (
-	"math/rand"
-
 	"github.com/v2ray/v2ray-core/app"
+	"github.com/v2ray/v2ray-core/common/dice"
 	"github.com/v2ray/v2ray-core/common/log"
 	v2net "github.com/v2ray/v2ray-core/common/net"
 	"github.com/v2ray/v2ray-core/common/retry"
@@ -46,8 +45,7 @@ func NewInboundDetourHandlerAlways(space app.Space, config *InboundDetourConfig)
 }
 
 func (this *InboundDetourHandlerAlways) GetConnectionHandler() (proxy.InboundConnectionHandler, int) {
-	idx := rand.Intn(len(this.ich))
-	ich := this.ich[idx]
+	ich := this.ich[dice.Roll(len(this.ich))]
 	return ich.handler, this.config.Allocation.Refresh
 }
 
diff --git a/transport/dialer/dialer.go b/transport/dialer/dialer.go
index fdbf05e36..306a7b92b 100644
--- a/transport/dialer/dialer.go
+++ b/transport/dialer/dialer.go
@@ -2,9 +2,9 @@ package dialer
 
 import (
 	"errors"
-	"math/rand"
 	"net"
 
+	"github.com/v2ray/v2ray-core/common/dice"
 	v2net "github.com/v2ray/v2ray-core/common/net"
 )
 
@@ -24,11 +24,7 @@ func Dial(dest v2net.Destination) (net.Conn, error) {
 		if len(ips) == 0 {
 			return nil, ErrInvalidHost
 		}
-		if len(ips) == 1 {
-			ip = ips[0]
-		} else {
-			ip = ips[rand.Intn(len(ips))]
-		}
+		ip = ips[dice.Roll(len(ips))]
 	}
 	if dest.IsTCP() {
 		return net.DialTCP("tcp", nil, &net.TCPAddr{
diff --git a/transport/dialer/dialer_test.go b/transport/dialer/dialer_test.go
index e3ffa1e10..358af891b 100644
--- a/transport/dialer/dialer_test.go
+++ b/transport/dialer/dialer_test.go
@@ -19,6 +19,7 @@ func TestDialDomain(t *testing.T) {
 	}
 	dest, err := server.Start()
 	assert.Error(err).IsNil()
+	defer server.Close()
 
 	conn, err := Dial(v2net.TCPDestination(v2net.DomainAddress("local.v2ray.com"), dest.Port()))
 	assert.Error(err).IsNil()