https://github.com/bluhm/smcroute/commit/3552c7db1bbd4b9c68d7b9aa27a08c575200bdb9

Index: src/inet.h
--- src/inet.h.orig
+++ src/inet.h
@@ -37,7 +37,7 @@
 typedef struct sockaddr_storage inet_addr_t;
 
 #ifndef s6_addr32
-# if   defined(__FreeBSD__)
+# if   defined(__FreeBSD__) || defined(__OpenBSD__)
 #  define s6_addr32 __u6_addr.__u6_addr32
 # elif defined(__linux__)
 #  define s6_addr32 __in6_u.__u6_addr32
