diff --git a/common/protocol/headers.go b/common/protocol/headers.go
index 83a5fdd6d..007ff5aa4 100644
--- a/common/protocol/headers.go
+++ b/common/protocol/headers.go
@@ -38,6 +38,8 @@ const (
 	RequestOptionChunkMasking bitmask.Byte = 0x04
 
 	RequestOptionGlobalPadding bitmask.Byte = 0x08
+
+	RequestOptionEarlyChecksum bitmask.Byte = 0x16
 )
 
 type RequestHeader struct {
diff --git a/proxy/vmess/encoding/server.go b/proxy/vmess/encoding/server.go
index 00cb31394..318326a5e 100644
--- a/proxy/vmess/encoding/server.go
+++ b/proxy/vmess/encoding/server.go
@@ -126,7 +126,7 @@ func parseSecurityType(b byte) protocol.SecurityType {
 func (s *ServerSession) DecodeRequestHeader(reader io.Reader) (*protocol.RequestHeader, error) {
 	buffer := buf.New()
 	behaviorRand := dice.NewDeterministicDice(int64(s.userValidator.GetBehaviorSeed()))
-	DrainSize := behaviorRand.Roll(3266) + 16 + 38 + dice.Roll(behaviorRand.Roll(64))
+	DrainSize := behaviorRand.Roll(3266) + 16 + 38 + dice.Roll(behaviorRand.Roll(64)+1)
 	readSizeRemain := DrainSize
 
 	drainConnection := func(e error) error {