diff --git a/third-party/libutp/utp_utils.cpp b/third-party/libutp/utp_utils.cpp
index 04758db10..5515e62a1 100644
--- a/third-party/libutp/utp_utils.cpp
+++ b/third-party/libutp/utp_utils.cpp
@@ -184,7 +184,7 @@ uint32 UTP_GetMilliseconds()
 
 #define UDP_IPV4_MTU (ETHERNET_MTU - IPV4_HEADER_SIZE - UDP_HEADER_SIZE - GRE_HEADER_SIZE - PPPOE_HEADER_SIZE - MPPE_HEADER_SIZE - FUDGE_HEADER_SIZE)
 #define UDP_IPV6_MTU (ETHERNET_MTU - IPV6_HEADER_SIZE - UDP_HEADER_SIZE - GRE_HEADER_SIZE - PPPOE_HEADER_SIZE - MPPE_HEADER_SIZE - FUDGE_HEADER_SIZE)
-#define UDP_TEREDO_MTU (TEREDO_MTU - UDP_HEADER_SIZE)
+#define UDP_TEREDO_MTU (TEREDO_MTU - IPV6_HEADER_SIZE - UDP_HEADER_SIZE)
 
 uint16 UTP_GetUDPMTU(const struct sockaddr *remote, socklen_t remotelen)
 {