diff --git a/platform/z1/contiki-conf.h b/platform/z1/contiki-conf.h
index 536b51913..af8b88cbb 100644
--- a/platform/z1/contiki-conf.h
+++ b/platform/z1/contiki-conf.h
@@ -222,7 +222,9 @@
 
 #define UIP_CONF_DHCP_LIGHT
 #define UIP_CONF_LLH_LEN                        0
+#ifndef UIP_CONF_RECEIVE_WINDOW
 #define UIP_CONF_RECEIVE_WINDOW                 48
+#endif
 #define UIP_CONF_TCP_MSS                        48
 #define UIP_CONF_MAX_CONNECTIONS                4
 #define UIP_CONF_MAX_LISTENPORTS                8