diff --git a/pico_bsd_sockets.h b/pico_bsd_sockets.h
index bda8cac..8f4c6bf 100644
--- a/pico_bsd_sockets.h
+++ b/pico_bsd_sockets.h
@@ -33,6 +33,7 @@ extern void   *pico_signal_tick;
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/in.h>
+    #include <netinet/tcp.h>
     #include <netdb.h>
     #include <fcntl.h>
     #include <sys/poll.h>