diff --git a/gold/link/crypto_test.go b/gold/link/crypto_test.go
index 8b3e58a..22b22be 100644
--- a/gold/link/crypto_test.go
+++ b/gold/link/crypto_test.go
@@ -5,6 +5,8 @@ import (
 	"crypto/rand"
 	"io"
 	"testing"
+
+	"golang.org/x/crypto/chacha20poly1305"
 )
 
 func TestXOR(t *testing.T) {
@@ -28,3 +30,22 @@ func TestXOR(t *testing.T) {
 		}
 	}
 }
+
+func TestXChacha20(t *testing.T) {
+	l := Link{}
+	k := make([]byte, 32)
+	_, err := rand.Read(k)
+	if err != nil {
+		t.Fatal(err)
+	}
+	l.aead, err = chacha20poly1305.NewX(k)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data := []byte("12345678")
+	for i := uint64(0); i < 100000; i++ {
+		if !bytes.Equal(l.DecodePreshared(uint16(i), l.EncodePreshared(uint16(i), data)), data) {
+			t.Fatal("unexpected preshared at", i, "addt", uint16(i))
+		}
+	}
+}
diff --git a/gold/link/send.go b/gold/link/send.go
index ae91c74..b3d5aea 100644
--- a/gold/link/send.go
+++ b/gold/link/send.go
@@ -72,7 +72,7 @@ func (l *Link) encrypt(p *head.Packet, sndcnt uint16, teatype uint8) {
 		logrus.Debugln("[send] data len after zstd:", len(p.Data))
 	}
 	if l.aead != nil {
-		p.Data = l.EncodePreshared(sndcnt, p.Data)
+		p.Data = l.EncodePreshared(sndcnt&0x0fff, p.Data)
 		logrus.Debugln("[send] data len after xchacha20:", len(p.Data))
 	}
 	p.Data = l.Encode(teatype, p.Data)