diff --git a/core/app.cpp b/core/app.cpp
index 9ec6f0b..fd457e5 100644
--- a/core/app.cpp
+++ b/core/app.cpp
@@ -43,6 +43,7 @@
 #include <arpa/inet.h>
 #include <utility>
 #include <fastcgi.h>
+#include <stddef.h>
 #include "app.h"
 #include "plugin.h"
 #include "misc.h"
@@ -1807,10 +1808,12 @@ int res;
 		return;
 
 	memset(&to, 0, sizeof(to));
-	to.sun_len = sizeof(to.sun_len)
-				+ sizeof(to.sun_family)
+
+	#ifdef __FreeBSD__
+	to.sun_len = offsetof(sockaddr_un, sun_path)
 				+ socket_to_send_on_exit.size()
 				+ 1; // terminating zero
+	#endif
 
 	to.sun_family = AF_UNIX;
 	snprintf(to.sun_path, sizeof(to.sun_path)/sizeof(char), "%s", socket_to_send_on_exit.c_str());