diff --git a/server.go b/server.go
index befe257..2b399d1 100644
--- a/server.go
+++ b/server.go
@@ -2,6 +2,7 @@ package mux
 
 import (
 	"context"
+	"github.com/sagernet/sing/common/debug"
 	"net"
 
 	"github.com/sagernet/sing/common/bufio"
@@ -112,11 +113,14 @@ func (s *Service) newConnection(ctx context.Context, sessionConn net.Conn, strea
 			}
 			err = SetBrutalOptions(sessionConn, sendBPS)
 			if err != nil {
-				err = WriteBrutalResponse(conn, 0, false, E.Cause(err, "enable TCP Brutal").Error())
-				if err != nil {
-					return E.Cause(err, "write brutal response")
+				// ignore error in test
+				if !debug.Enabled {
+					err = WriteBrutalResponse(conn, 0, false, E.Cause(err, "enable TCP Brutal").Error())
+					if err != nil {
+						return E.Cause(err, "write brutal response")
+					}
+					return nil
 				}
-				return nil
 			}
 			err = WriteBrutalResponse(conn, s.brutal.ReceiveBPS, true, "")
 			if err != nil {