diff --git a/src/include/lwip/netbuf.h b/src/include/lwip/netbuf.h
index 969ed1b1..64c31645 100644
--- a/src/include/lwip/netbuf.h
+++ b/src/include/lwip/netbuf.h
@@ -99,7 +99,7 @@ LWIP_NETCONN_SCOPE void              netbuf_first    (struct netbuf *buf);
 #define netbuf_set_destaddr(buf, destaddr) ip_addr_set(&((buf)->toaddr), destaddr)
 #if LWIP_CHECKSUM_ON_COPY
 #define netbuf_destport(buf)         (((buf)->flags & NETBUF_FLAG_DESTADDR) ? (buf)->toport_chksum : 0)
-#else
+#else /* LWIP_CHECKSUM_ON_COPY */
 #define netbuf_destport(buf)         ((buf)->toport_chksum)
 #endif /* LWIP_CHECKSUM_ON_COPY */
 #endif /* LWIP_NETBUF_RECVINFO */