diff --git a/moo/configure b/moo/configure
index 98f36d1..08243ac 100755
--- a/moo/configure
+++ b/moo/configure
@@ -21357,6 +21357,25 @@ $as_echo "#define MOO_SA_FAMILY_T_IS_SIGNED 1" >>confdefs.h
  fi
 
 	fi
+
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking offset of sa_family in struct sockaddr" >&5
+$as_echo_n "checking offset of sa_family in struct sockaddr... " >&6; }
+	if ac_fn_c_compute_int "$LINENO" "offsetof(struct sockaddr, sa_family)" "ac_cv_offsetof_sa_family"        "#include <stddef.h>
+		 #include <winsock2.h>
+		 #include <ws2tcpip.h>"; then :
+
+else
+  ac_cv_offsteof_sa_family=0
+fi
+
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_offsetof_sa_family" >&5
+$as_echo "$ac_cv_offsetof_sa_family" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define MOO_OFFSETOF_SA_FAMILY ${ac_cv_offsetof_sa_family}
+_ACEOF
+
+
 else
 	# The cast to long int works around a bug in the HP C Compiler
 # version HP92453-01 B.11.11.23709.GP, which incorrectly rejects
@@ -21704,6 +21723,24 @@ $as_echo "#define MOO_SA_FAMILY_T_IS_SIGNED 1" >>confdefs.h
  fi
 
 	fi
+
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking offset of sa_family in struct sockaddr" >&5
+$as_echo_n "checking offset of sa_family in struct sockaddr... " >&6; }
+	if ac_fn_c_compute_int "$LINENO" "offsetof(struct sockaddr, sa_family)" "ac_cv_offsetof_sa_family"        "#include <stddef.h>
+		 #include <sys/types.h>
+		 #include <sys/socket.h>"; then :
+
+else
+  ac_cv_offsteof_sa_family=0
+fi
+
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_offsetof_sa_family" >&5
+$as_echo "$ac_cv_offsetof_sa_family" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define MOO_OFFSETOF_SA_FAMILY ${ac_cv_offsetof_sa_family}
+_ACEOF
+
 fi
 
 if test ${ac_cv_sizeof___int128_t} -gt 0
diff --git a/moo/configure.ac b/moo/configure.ac
index 5d46f23..ad9d667 100644
--- a/moo/configure.ac
+++ b/moo/configure.ac
@@ -369,6 +369,16 @@ then
 			[#include <winsock2.h>
 			 #include <ws2tcpip.h>])
 	fi
+
+	AC_MSG_CHECKING([offset of sa_family in struct sockaddr])
+	AC_COMPUTE_INT([ac_cv_offsetof_sa_family],
+		[[offsetof(struct sockaddr, sa_family)]],
+		[#include <stddef.h>
+		 #include <winsock2.h>
+		 #include <ws2tcpip.h>], [ac_cv_offsteof_sa_family=0])
+	AC_MSG_RESULT([$ac_cv_offsetof_sa_family])
+	AC_DEFINE_UNQUOTED(MOO_OFFSETOF_SA_FAMILY, ${ac_cv_offsetof_sa_family}, [offsetof(struct sockaddr, sa_family)])
+
 else
 	AC_CHECK_SIZEOF(struct sockaddr_in,,[
 		#include <sys/types.h>
@@ -417,6 +427,15 @@ else
 			 #include <sys/socket.h>
 			 #include <netinet/in.h>])
 	fi
+
+	AC_MSG_CHECKING([offset of sa_family in struct sockaddr])
+	AC_COMPUTE_INT([ac_cv_offsetof_sa_family],
+		[[offsetof(struct sockaddr, sa_family)]],
+		[#include <stddef.h>
+		 #include <sys/types.h>
+		 #include <sys/socket.h>], [ac_cv_offsteof_sa_family=0])
+	AC_MSG_RESULT([$ac_cv_offsetof_sa_family])
+	AC_DEFINE_UNQUOTED(MOO_OFFSETOF_SA_FAMILY, ${ac_cv_offsetof_sa_family}, [offsetof(struct sockaddr, sa_family)])
 fi
 
 dnl gcc 3.4.3 on opensolaris x86 gave this warning without -msse or 
diff --git a/moo/lib/moo-cfg.h.in b/moo/lib/moo-cfg.h.in
index d4887b8..77eb36b 100644
--- a/moo/lib/moo-cfg.h.in
+++ b/moo/lib/moo-cfg.h.in
@@ -416,6 +416,9 @@
 /* MB_LEN_MAX */
 #undef MOO_MBLEN_MAX
 
+/* offsetof(struct sockaddr, sa_family) */
+#undef MOO_OFFSETOF_SA_FAMILY
+
 /* Author */
 #undef MOO_PACKAGE_AUTHOR
 
diff --git a/moo/mod/_sck.h b/moo/mod/_sck.h
index 246848e..90275af 100644
--- a/moo/mod/_sck.h
+++ b/moo/mod/_sck.h
@@ -102,6 +102,9 @@ struct sck_t
 
 struct sck_addr_t
 {
+#if defined(MOO_OFFSETOF_SA_FAMILY) && (MOO_OFFSETOF_SA_FAMILY > 0)
+	moo_uint8_t filler[MOO_OFFSETOF_SA_FAMILY];
+#endif
 	sck_addr_family_t family;
 	moo_uint8_t data[1];
 };