diff --git a/common/bufio/buffer.go b/common/bufio/buffer.go
index 4f9ee94..30f4c1e 100644
--- a/common/bufio/buffer.go
+++ b/common/bufio/buffer.go
@@ -3,6 +3,7 @@ package bufio
 import (
 	"io"
 	"os"
+	"sync"
 
 	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/buf"
@@ -75,6 +76,7 @@ func (r *BufferedReader) Upstream() any {
 type BufferedWriter struct {
 	upstream io.Writer
 	buffer   *buf.Buffer
+	access   sync.Mutex
 }
 
 func NewBufferedWriter(upstream io.Writer, buffer *buf.Buffer) *BufferedWriter {
@@ -85,6 +87,11 @@ func NewBufferedWriter(upstream io.Writer, buffer *buf.Buffer) *BufferedWriter {
 }
 
 func (w *BufferedWriter) Write(p []byte) (n int, err error) {
+	w.access.Lock()
+	defer w.access.Unlock()
+	if w.buffer == nil {
+		return w.upstream.Write(p)
+	}
 	for {
 		var writeN int
 		writeN, err = w.buffer.Write(p[n:])
@@ -100,6 +107,30 @@ func (w *BufferedWriter) Write(p []byte) (n int, err error) {
 	}
 }
 
+func (w *BufferedWriter) Fallthrough() error {
+	w.access.Lock()
+	defer w.access.Unlock()
+	if w.buffer == nil {
+		return nil
+	}
+	if !w.buffer.IsEmpty() {
+		_, err := w.upstream.Write(w.buffer.Bytes())
+		if err != nil {
+			return err
+		}
+	}
+	w.buffer.Release()
+	w.buffer = nil
+	return nil
+}
+
 func (w *BufferedWriter) ReadFrom(r io.Reader) (n int64, err error) {
+	if w.buffer == nil {
+		return Copy(w.upstream, r)
+	}
 	return CopyExtendedBuffer(NewExtendedWriter(w), NewExtendedReader(r), w.buffer)
 }
+
+func (w *BufferedWriter) WriterReplaceable() bool {
+	return w.buffer == nil
+}