diff --git a/socket/socket_getifname.c b/socket/socket_getifname.c
index 1902fd5..1afe210 100644
--- a/socket/socket_getifname.c
+++ b/socket/socket_getifname.c
@@ -7,6 +7,11 @@
 #include "haven2i.h"
 
 #ifdef HAVE_N2I
+/* legacy BSD name */
+#ifndef IF_NAMESIZE
+#define IF_NAMESIZE IFNAMSIZ
+#endif
+
 static char ifname[IF_NAMESIZE];
 
 const char* socket_getifname(uint32 _interface) {