--- lwip-2.0.2/src/include/lwip/opt.h   (original)
+++ lwip-2.0.2/src/include/lwip/opt.h   (patched)
@@ -455,6 +455,14 @@
 #endif
 
 /**
+ * MEMP_NUM_SELECT_CB: the number of struct lwip_select_cb.
+ * (only needed if you use the sequential API, like api_lib.c)
+ */
+#if !defined MEMP_NUM_SELECT_CB || defined __DOXYGEN__
+#define MEMP_NUM_SELECT_CB              4
+#endif
+
+/**
  * MEMP_NUM_TCPIP_MSG_API: the number of struct tcpip_msg, which are used
  * for callback/timeout API communication.
  * (only needed if you use tcpip.c)