diff --git a/src/include/lwip/priv/tcp_priv.h b/src/include/lwip/priv/tcp_priv.h
index 86b31fa3..72f9126d 100644
--- a/src/include/lwip/priv/tcp_priv.h
+++ b/src/include/lwip/priv/tcp_priv.h
@@ -302,10 +302,10 @@ struct tcp_seg {
 #endif
 
 #define LWIP_TCP_OPT_LENGTH(flags) \
-  (flags & TF_SEG_OPTS_MSS       ? LWIP_TCP_OPT_LEN_MSS           : 0) + \
-  (flags & TF_SEG_OPTS_TS        ? LWIP_TCP_OPT_LEN_TS_OUT        : 0) + \
-  (flags & TF_SEG_OPTS_WND_SCALE ? LWIP_TCP_OPT_LEN_WS_OUT        : 0) + \
-  (flags & TF_SEG_OPTS_SACK_PERM ? LWIP_TCP_OPT_LEN_SACK_PERM_OUT : 0)
+  ((flags) & TF_SEG_OPTS_MSS       ? LWIP_TCP_OPT_LEN_MSS           : 0) + \
+  ((flags) & TF_SEG_OPTS_TS        ? LWIP_TCP_OPT_LEN_TS_OUT        : 0) + \
+  ((flags) & TF_SEG_OPTS_WND_SCALE ? LWIP_TCP_OPT_LEN_WS_OUT        : 0) + \
+  ((flags) & TF_SEG_OPTS_SACK_PERM ? LWIP_TCP_OPT_LEN_SACK_PERM_OUT : 0)
 
 /** This returns a TCP header option for MSS in an u32_t */
 #define TCP_BUILD_MSS_OPTION(mss) lwip_htonl(0x02040000 | ((mss) & 0xFFFF))