diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index c4c2c8a2..0762afc2 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -40,6 +40,7 @@
 #include "lwip/tcpip.h"
 #include "lwip/memp.h"
 
+#if !NO_SYS
 
 struct
 netbuf *netbuf_new(void)
@@ -689,3 +690,4 @@ netconn_err(struct netconn *conn)
   return conn->err;
 }
 
+#endif /* !NO_SYS */
diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index 077ed3a9..81f5e927 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -38,6 +38,8 @@
 #include "lwip/tcpip.h"
 #include "lwip/igmp.h"
 
+#if !NO_SYS
+
 #if LWIP_RAW
 static u8_t
 recv_raw(void *arg, struct raw_pcb *pcb, struct pbuf *p,
@@ -746,3 +748,5 @@ do_join_leave_group(struct api_msg_msg *msg)
   sys_mbox_post(msg->conn->mbox, NULL);
 }
 #endif /* LWIP_IGMP */
+
+#endif /* !NO_SYS */
diff --git a/src/api/sockets.c b/src/api/sockets.c
index 06a78d3d..1edf50f8 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -44,6 +44,8 @@
 #include "lwip/inet.h"
 #include "lwip/tcp.h"
 
+#if !NO_SYS
+
 #define NUM_SOCKETS MEMP_NUM_NETCONN
 
 struct lwip_socket {
@@ -1432,3 +1434,4 @@ int lwip_ioctl(int s, long cmd, void *argp)
   }
 }
 
+#endif /* !NO_SYS */
diff --git a/src/api/tcpip.c b/src/api/tcpip.c
index 94f82dd9..d0f07fbf 100644
--- a/src/api/tcpip.c
+++ b/src/api/tcpip.c
@@ -47,6 +47,8 @@
 #include "lwip/tcpip.h"
 #include "lwip/igmp.h"
 
+#if !NO_SYS
+
 static void (* tcpip_init_done)(void *arg) = NULL;
 static void *tcpip_init_done_arg           = NULL;
 static sys_mbox_t mbox                     = SYS_MBOX_NULL;
@@ -368,3 +370,4 @@ tcpip_init(void (* initfunc)(void *), void *arg)
   sys_thread_new(tcpip_thread, NULL, TCPIP_THREAD_PRIO);
 }
 
+#endif /* !NO_SYS */