diff --git a/shadowsocks/tcprelay.py b/shadowsocks/tcprelay.py
index f73f842..97d8594 100644
--- a/shadowsocks/tcprelay.py
+++ b/shadowsocks/tcprelay.py
@@ -232,11 +232,15 @@ class TCPRelayHandler(object):
                 #logging.info('UDP over TCP sendto %d %s' % (len(data), binascii.hexlify(data)))
                 while len(self._udp_data_send_buffer) > 6:
                     length = struct.unpack('>H', self._udp_data_send_buffer[:2])[0]
+                    if length >= 0xff00:
+                        length = struct.unpack('>H', self._udp_data_send_buffer[1:3])[0] + 0xff00
 
                     if length > len(self._udp_data_send_buffer):
                         break
 
                     data = self._udp_data_send_buffer[:length]
+                    if length >= 0xff00:
+                        data = data[1:]
                     self._udp_data_send_buffer = self._udp_data_send_buffer[length:]
 
                     frag = common.ord(data[2])
@@ -660,7 +664,11 @@ class TCPRelayHandler(object):
                 except Exception as e:
                     ip = socket.inet_pton(socket.AF_INET6, addr[0])
                     data = b'\x00\x04' + ip + port + data
-                data = struct.pack('>H', len(data) + 2) + data
+                size = len(data) + 2
+                if size >= 0xff00:
+                    data = common.chr(0xff) + struct.pack('>H', size - 0xff00 + 1) + data
+                else:
+                    data = struct.pack('>H', size) + data
                 #logging.info('UDP over TCP recvfrom %s:%d %d bytes to %s:%d' % (addr[0], addr[1], len(data), self._client_address[0], self._client_address[1]))
             else:
                 data = self._remote_sock.recv(BUF_SIZE)