diff --git a/adat/adat.c b/adat/adat.c
index 35607eb51..bc02794f2 100644
--- a/adat/adat.c
+++ b/adat/adat.c
@@ -21,8 +21,6 @@
 //   License along with this library; if not, write to the Free Software
 //   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #  include "config.h"
 #endif
diff --git a/aor/ar3030.c b/aor/ar3030.c
index 76c4f3c8d..1570db05f 100644
--- a/aor/ar3030.c
+++ b/aor/ar3030.c
@@ -18,8 +18,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/barrett/barrett.c b/barrett/barrett.c
index 6ec06adf4..a0c39c145 100644
--- a/barrett/barrett.c
+++ b/barrett/barrett.c
@@ -18,8 +18,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #  include "config.h"
 #endif
diff --git a/configure.ac b/configure.ac
index e252ad6d8..7646bf2d9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -27,6 +27,8 @@ AC_CONFIG_HEADERS([include/config.h])
 dnl Place build system provided programs in this directory.
 AC_CONFIG_AUX_DIR([build-aux])
 
+AC_USE_SYSTEM_EXTENSIONS
+
 
 ## ------------------------ ##
 ## Automake Initialisation. ##
@@ -299,6 +301,7 @@ AS_CASE(["$host_os"],
 
 dnl Check if C99 struct initializers are supported
 AC_MSG_CHECKING([whether C99 struct/array initializers are supported])
+
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],
                   [[struct{char a;int b;}s[8]={[3]={.b=5}};]])],
                   [AC_MSG_RESULT(yes)],
@@ -307,7 +310,6 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],
 "Have you considered GCC lately?."])
                   ])
 
-
 dnl Check for libusb, treat LIBUSB_LIBS and LIBUSB_CFLAGS as precious variables
 AC_MSG_CHECKING([whether to build USB dependent backends])
 AC_ARG_WITH([libusb],
diff --git a/dummy/dummy.c b/dummy/dummy.c
index ddd48bbba..0b2072e9a 100644
--- a/dummy/dummy.c
+++ b/dummy/dummy.c
@@ -19,8 +19,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/dummy/flrig.c b/dummy/flrig.c
index d7ee4d5b5..2b84d460f 100644
--- a/dummy/flrig.c
+++ b/dummy/flrig.c
@@ -19,8 +19,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 500
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/elad/elad.c b/elad/elad.c
index 0d4b43a9f..95aaef41e 100644
--- a/elad/elad.c
+++ b/elad/elad.c
@@ -21,8 +21,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/icom/optoscan.c b/icom/optoscan.c
index 3ce568f8c..af1db8b92 100644
--- a/icom/optoscan.c
+++ b/icom/optoscan.c
@@ -18,8 +18,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/kenwood/kenwood.c b/kenwood/kenwood.c
index bc3d70169..4629c2ee0 100644
--- a/kenwood/kenwood.c
+++ b/kenwood/kenwood.c
@@ -20,8 +20,6 @@
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/pcr/pcr.c b/pcr/pcr.c
index 8a3d08a53..cf9555799 100644
--- a/pcr/pcr.c
+++ b/pcr/pcr.c
@@ -28,8 +28,6 @@
  * (403) PCR1500 fw 2.0, proto 2.0 (usb) by KM3T
  *
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
diff --git a/tentec/orion.c b/tentec/orion.c
index 77430e24d..30060f997 100644
--- a/tentec/orion.c
+++ b/tentec/orion.c
@@ -65,8 +65,6 @@
  * This backend supports the Ten-Tec Orion (565) and Orion II (566) transceivers.
  * \n This backend tested mostly with firmware versions 1.372 and 2.062a
  */
-#define _XOPEN_SOURCE 600
-
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif