diff --git a/common/crypto/auth.go b/common/crypto/auth.go
index 84f5b41a..41664531 100644
--- a/common/crypto/auth.go
+++ b/common/crypto/auth.go
@@ -204,7 +204,7 @@ func (w *AuthenticationWriter) writeStream(mb buf.MultiBuffer) error {
 func (w *AuthenticationWriter) writePacket(mb buf.MultiBuffer) error {
 	defer mb.Release()
 
-	mb2Write := buf.NewMultiBufferCap(len(mb) * 2)
+	mb2Write := buf.NewMultiBufferCap(len(mb) + 1)
 
 	for {
 		b := mb.SplitFirst()