diff --git a/main.go b/main.go
index cd4ec4f..4e7f1a6 100644
--- a/main.go
+++ b/main.go
@@ -10,10 +10,10 @@ import (
 	"net"
 	"net/netip"
 	"sync"
+	"syscall"
 
 	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
-	"golang.org/x/sys/unix"
 )
 
 const (
@@ -21,7 +21,7 @@ const (
 )
 
 var (
-	OOB_SIZE = unix.CmsgSpace(16 + 2) // ipv6 address + port
+	OOB_SIZE = syscall.CmsgSpace(syscall.SizeofInet6Pktinfo) // ipv6 address + iface index, struct in6_pktinfo
 )
 
 func (vx *vx46) transform46(msgs4 []ipv4.Message, msgs6 []ipv6.Message) error {