Here it is my code: union sockaddr46 { sockaddr_in sockv4; sockaddr_in6 sockv6; }; and here it is what I get: prova.c:16: error: parse error before "sockaddr_in" prova.c:16: warning: no semicolon at end of struct or union prova.c:17: warning: data definition has no type or storage class (the file is called prova.c) If I cancel the sockaddr and I put 2 int in there, everything works fine. What am I doing wrong? Praise ps: using suse 8.2