diff --git a/socket/socket_sctp6b.c b/socket/socket_sctp6b.c
index 8995eb8..9e107e4 100644
--- a/socket/socket_sctp6b.c
+++ b/socket/socket_sctp6b.c
@@ -1,3 +1,4 @@
+#define _POSIX_SOURCE
 #include <sys/types.h>
 #ifndef __MINGW32__
 #include <unistd.h>
diff --git a/socket/socket_tcp6b.c b/socket/socket_tcp6b.c
index 2910212..f563b5b 100644
--- a/socket/socket_tcp6b.c
+++ b/socket/socket_tcp6b.c
@@ -1,3 +1,4 @@
+#define _POSIX_SOURCE
 #include <sys/types.h>
 #ifndef __MINGW32__
 #include <unistd.h>
diff --git a/socket/socket_udp6.c b/socket/socket_udp6.c
index 72b3971..b34df7f 100644
--- a/socket/socket_udp6.c
+++ b/socket/socket_udp6.c
@@ -1,3 +1,4 @@
+#define _POSIX_SOURCE
 #include <sys/types.h>
 #ifndef __MINGW32__
 #include <unistd.h>