diff --git a/stack_gvisor_udp.go b/stack_gvisor_udp.go
index ce4648b..ca5856a 100644
--- a/stack_gvisor_udp.go
+++ b/stack_gvisor_udp.go
@@ -90,7 +90,7 @@ func (w *UDPBackWriter) WritePacket(packetBuffer *buf.Buffer, destination M.Sock
 		return E.Cause(os.ErrInvalid, "invalid destination")
 	} else if destination.IsIPv4() && w.sourceNetwork == header.IPv6ProtocolNumber {
 		destination = M.SocksaddrFrom(netip.AddrFrom16(destination.Addr.As16()), destination.Port)
-	} else if destination.IsIPv6() && (w.sourceNetwork == header.IPv4AddressSizeBits) {
+	} else if destination.IsIPv6() && (w.sourceNetwork == header.IPv4ProtocolNumber) {
 		return E.New("send IPv6 packet to IPv4 connection")
 	}