diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index e95da5f7..9edcf169 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -349,7 +349,7 @@ void             tcp_err     (struct tcp_pcb *pcb, tcp_err_fn err);
 #define          tcp_sndbuf(pcb)          (TCPWND16((pcb)->snd_buf))
 #define          tcp_sndqueuelen(pcb)     ((pcb)->snd_queuelen)
 #define          tcp_nagle_disable(pcb)   ((pcb)->flags |= TF_NODELAY)
-#define          tcp_nagle_enable(pcb)    ((pcb)->flags = (u16_t)((pcb)->flags & ~TF_NODELAY))
+#define          tcp_nagle_enable(pcb)    ((pcb)->flags = (tcpflags_t)((pcb)->flags & ~TF_NODELAY))
 #define          tcp_nagle_disabled(pcb)  (((pcb)->flags & TF_NODELAY) != 0)
 
 #if TCP_LISTEN_BACKLOG