diff --git a/src/include/lwip/tcpip.h b/src/include/lwip/tcpip.h
index 3b08da2e..604b2ea4 100644
--- a/src/include/lwip/tcpip.h
+++ b/src/include/lwip/tcpip.h
@@ -40,6 +40,7 @@
 #include "lwip/netifapi.h"
 #include "lwip/pbuf.h"
 #include "lwip/api.h"
+#include "lwip/sys.h"
 
 #ifdef __cplusplus
 extern "C" {