diff --git a/stack_gvisor_tcp.go b/stack_gvisor_tcp.go
index 1592799..0c63ee1 100644
--- a/stack_gvisor_tcp.go
+++ b/stack_gvisor_tcp.go
@@ -52,7 +52,7 @@ func (f *TCPForwarder) HandlePacket(id stack.TransportEndpointID, pkt *stack.Pac
 			ipHdr.SetSourceAddressWithChecksumUpdate(inet4LoopbackAddress)
 			tcpHdr := header.TCP(pkt.TransportHeader().Slice())
 			tcpHdr.SetChecksum(0)
-			tcpHdr.SetChecksum(^checksum.Checksum(tcpHdr.Payload(), tcpHdr.CalculateChecksum(
+			tcpHdr.SetChecksum(^checksum.Combine(pkt.Data().Checksum(), tcpHdr.CalculateChecksum(
 				header.PseudoHeaderChecksum(header.TCPProtocolNumber, ipHdr.SourceAddress(), ipHdr.DestinationAddress(), ipHdr.PayloadLength()),
 			)))
 			f.tun.WritePacket(pkt)
@@ -66,7 +66,7 @@ func (f *TCPForwarder) HandlePacket(id stack.TransportEndpointID, pkt *stack.Pac
 			ipHdr.SetSourceAddress(inet6LoopbackAddress)
 			tcpHdr := header.TCP(pkt.TransportHeader().Slice())
 			tcpHdr.SetChecksum(0)
-			tcpHdr.SetChecksum(^checksum.Checksum(tcpHdr.Payload(), tcpHdr.CalculateChecksum(
+			tcpHdr.SetChecksum(^checksum.Combine(pkt.Data().Checksum(), tcpHdr.CalculateChecksum(
 				header.PseudoHeaderChecksum(header.TCPProtocolNumber, ipHdr.SourceAddress(), ipHdr.DestinationAddress(), ipHdr.PayloadLength()),
 			)))
 			f.tun.WritePacket(pkt)