diff --git a/configure.ac b/configure.ac
index 63986ab7..385d16f7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7,6 +7,7 @@ AC_CONFIG_AUX_DIR([build-aux])
 AM_INIT_AUTOMAKE([1.11 -Wno-portability foreign no-define tar-ustar no-dist-gzip dist-xz])
 AM_MAINTAINER_MODE([enable])
 AM_SILENT_RULES([yes])
+AC_USE_SYSTEM_EXTENSIONS
 AC_SYS_LARGEFILE
 
 AC_PROG_CC
diff --git a/src/libostree/ostree-core.c b/src/libostree/ostree-core.c
index fe76bd46..4e9fdf98 100644
--- a/src/libostree/ostree-core.c
+++ b/src/libostree/ostree-core.c
@@ -20,9 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-/* for mkdtemp */
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include "ostree.h"
diff --git a/src/libostree/ostree-diff.c b/src/libostree/ostree-diff.c
index 0a8222da..560ac808 100644
--- a/src/libostree/ostree-diff.c
+++ b/src/libostree/ostree-diff.c
@@ -20,8 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include "ostree.h"
diff --git a/src/libostree/ostree-repo-traverse.c b/src/libostree/ostree-repo-traverse.c
index 70b22d7a..6838314d 100644
--- a/src/libostree/ostree-repo-traverse.c
+++ b/src/libostree/ostree-repo-traverse.c
@@ -20,8 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include "ostree.h"
diff --git a/src/libotutil/ot-unix-utils.c b/src/libotutil/ot-unix-utils.c
index 54c5ac14..8cb19926 100644
--- a/src/libotutil/ot-unix-utils.c
+++ b/src/libotutil/ot-unix-utils.c
@@ -22,8 +22,6 @@
 
 #include "config.h"
 
-#define _GNU_SOURCE
-
 #include "otutil.h"
 
 #include <gio/gio.h>
diff --git a/src/ostree/ot-admin-cleanup.c b/src/ostree/ot-admin-cleanup.c
index d8d9e8e3..9c2560f3 100644
--- a/src/ostree/ot-admin-cleanup.c
+++ b/src/ostree/ot-admin-cleanup.c
@@ -20,7 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
 #include "config.h"
 
 #include "ot-admin-functions.h"
diff --git a/src/ostree/ot-admin-functions.c b/src/ostree/ot-admin-functions.c
index 3780c2a9..4c3cb49d 100644
--- a/src/ostree/ot-admin-functions.c
+++ b/src/ostree/ot-admin-functions.c
@@ -20,7 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
 #include "config.h"
 
 #include "ot-admin-functions.h"
diff --git a/src/ostree/ot-admin-util.c b/src/ostree/ot-admin-util.c
index 871871fd..affe6db0 100644
--- a/src/ostree/ot-admin-util.c
+++ b/src/ostree/ot-admin-util.c
@@ -20,7 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
 #include "config.h"
 
 #include "ot-admin-functions.h"
diff --git a/src/switchroot/ostree-mount-util.c b/src/switchroot/ostree-mount-util.c
index c993c238..c6df559c 100644
--- a/src/switchroot/ostree-mount-util.c
+++ b/src/switchroot/ostree-mount-util.c
@@ -20,7 +20,7 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
+#include "config.h"
 
 #include <stdarg.h>
 #include <errno.h>
diff --git a/src/switchroot/ostree-prepare-root.c b/src/switchroot/ostree-prepare-root.c
index cc885d3c..a77da7c6 100644
--- a/src/switchroot/ostree-prepare-root.c
+++ b/src/switchroot/ostree-prepare-root.c
@@ -23,7 +23,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-#define _GNU_SOURCE
+
+#include "config.h"
+
 #include <sys/mount.h>
 #include <sys/types.h>
 #include <sys/stat.h>
diff --git a/src/switchroot/ostree-remount.c b/src/switchroot/ostree-remount.c
index ff5a06da..6dbeecc0 100644
--- a/src/switchroot/ostree-remount.c
+++ b/src/switchroot/ostree-remount.c
@@ -20,7 +20,7 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
+#include "config.h"
 
 #include <string.h>
 #include <stdio.h>