diff --git a/platform/cc2538dk/contiki-conf.h b/platform/cc2538dk/contiki-conf.h
index a2a23eca3..86e8bd3fc 100644
--- a/platform/cc2538dk/contiki-conf.h
+++ b/platform/cc2538dk/contiki-conf.h
@@ -318,7 +318,9 @@ typedef uint32_t rtimer_clock_t;
 #ifndef UIP_CONF_TCP
 #define UIP_CONF_TCP                         1
 #endif
+#ifndef UIP_CONF_TCP_MSS
 #define UIP_CONF_TCP_MSS                    64
+#endif
 #define UIP_CONF_UDP                         1
 #define UIP_CONF_UDP_CHECKSUMS               1
 #define UIP_CONF_ICMP6                       1