diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index f7f19c5b..3acee1ca 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -600,7 +600,9 @@ netconn_alloc(enum netconn_type t, netconn_callback callback)
   conn->acceptmbox   = SYS_MBOX_NULL;
   conn->state        = NETCONN_NONE;
   /* initialize socket to -1 since 0 is a valid socket */
+#if LWIP_SOCKET
   conn->socket       = -1;
+#endif /* LWIP_SOCKET */
   conn->callback     = callback;
   conn->recv_avail   = 0;
 #if LWIP_TCP
diff --git a/src/include/lwip/api.h b/src/include/lwip/api.h
index cc2fb288..9c402e97 100644
--- a/src/include/lwip/api.h
+++ b/src/include/lwip/api.h
@@ -151,7 +151,9 @@ struct netconn {
       by the application thread */
   sys_mbox_t acceptmbox;
   /** only used for socket layer */
+#if LWIP_SOCKET
   int socket;
+#endif /* LWIP_SOCKET */
 #if LWIP_SO_RCVTIMEO
   /** timeout to wait for new data to be received
       (or connections to arrive for listening netconns) */
@@ -162,7 +164,12 @@ struct netconn {
       not used for TCP: adjust TCP_WND instead! */
   int recv_bufsize;
 #endif /* LWIP_SO_RCVBUF */
+  /** number of bytes currently in recvmbox to be received,
+      tested against recv_bufsize to limit bytes on recvmbox
+      for UDP and RAW
+      @todo: should only be necessary with LWIP_SO_RCVBUF==1 */
   s16_t recv_avail;
+  /** flags holding more netconn-internal state, see NETCONN_FLAG_* defines */
   u8_t flags;
 #if LWIP_TCP
   /** TCP: when data passed to netconn_write doesn't fit into the send buffer,