diff --git a/src/core/tcp.c b/src/core/tcp.c
index b4054bae..16536ce6 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -73,6 +73,13 @@
 #define TCP_KEEP_INTVL(pcb) TCP_KEEPINTVL_DEFAULT
 #endif /* LWIP_TCP_KEEPALIVE */
 
+/* As initial send MSS, we use TCP_MSS but limit it to 536. */
+#if TCP_MSS > 536
+#define INITIAL_MSS 536
+#else
+#define INITIAL_MSS TCP_MSS
+#endif
+
 const char * const tcp_state_str[] = {
   "CLOSED",
   "LISTEN",
@@ -868,7 +875,7 @@ tcp_connect(struct tcp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port,
   pcb->snd_wnd = TCP_WND;
   /* As initial send MSS, we use TCP_MSS but limit it to 536.
      The send MSS is updated when an MSS option is received. */
-  pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
+  pcb->mss = INITIAL_MSS;
 #if TCP_CALCULATE_EFF_SEND_MSS
   pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip);
 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
@@ -1524,7 +1531,7 @@ tcp_alloc(u8_t prio)
     pcb->ttl = TCP_TTL;
     /* As initial send MSS, we use TCP_MSS but limit it to 536.
        The send MSS is updated when an MSS option is received. */
-    pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
+    pcb->mss = INITIAL_MSS;
     pcb->rto = 3000 / TCP_SLOW_INTERVAL;
     pcb->sv = 3000 / TCP_SLOW_INTERVAL;
     pcb->rtime = -1;