Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -179,10 +179,24 @@
 AS_IF([test x"$PLUGIN_SUFFIX" != x""], [
 	AC_SUBST(USE_SRCS_PLUGINS, '${SRCS_PLUGINS}')
 	AC_SUBST(TESTPLUGIN, "plugin")
 	AC_DEFINE(OF_HAVE_PLUGINS, 1, [Whether we have plugin support])
 ])
+
+AC_MSG_CHECKING(whether we need -D_GNU_SOURCE)
+AC_EGREP_CPP(yes, [
+	#include <stdlib.h>
+
+	#ifdef __GLIBC__
+	yes
+	#endif
+], [
+	CPPFLAGS="-D_GNU_SOURCE $CPPFLAGS"
+	AC_MSG_RESULT(yes)
+], [
+	AC_MSG_RESULT(no)
+])
 
 objc_runtime="ObjFW runtime"
 AC_CHECK_HEADER(objc/objc.h)
 AC_MSG_CHECKING(which Objective C runtime to use)
 AC_ARG_ENABLE(runtime,

Index: src/OFDate.m
==================================================================
--- src/OFDate.m
+++ src/OFDate.m
@@ -12,13 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _POSIX_C_SOURCE 199309L
-#define _XOPEN_SOURCE 500
-
 #include "config.h"
 
 #include <stdint.h>
 #include <limits.h>
 #include <time.h>

Index: src/OFFile.m
==================================================================
--- src/OFFile.m
+++ src/OFFile.m
@@ -12,16 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _POSIX_C_SOURCE 200112L
-#define _XOPEN_SOURCE 600
-#define _BSD_SOURCE
-#define _NETBSD_SOURCE
-#define _DARWIN_C_SOURCE
-#define __BSD_VISIBLE 1
 #define __NO_EXT_QNX
 
 #include "config.h"
 
 /* Work around a bug with Clang + glibc */

Index: src/OFMapTable.m
==================================================================
--- src/OFMapTable.m
+++ src/OFMapTable.m
@@ -12,12 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _BSD_SOURCE
-
 #include "config.h"
 
 #include <string.h>
 
 #include <assert.h>

Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -12,12 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _BSD_SOURCE
-
 #include "config.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

Index: src/OFProcess.m
==================================================================
--- src/OFProcess.m
+++ src/OFProcess.m
@@ -12,12 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _POSIX_SOURCE
-
 #include "config.h"
 
 #include <string.h>
 
 #ifndef _WIN32

Index: src/OFThread.m
==================================================================
--- src/OFThread.m
+++ src/OFThread.m
@@ -13,12 +13,10 @@
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
 #define OF_THREAD_M
-#define _POSIX_C_SOURCE 200112L
-#define _POSIX_TIMERS
 #define __NO_EXT_QNX
 
 #include "config.h"
 
 #include <stdlib.h>

Index: src/exceptions/OFAddressTranslationFailedException.m
==================================================================
--- src/exceptions/OFAddressTranslationFailedException.m
+++ src/exceptions/OFAddressTranslationFailedException.m
@@ -12,12 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _BSD_SOURCE
-
 #include "config.h"
 
 #import "OFAddressTranslationFailedException.h"
 #import "OFString.h"
 

Index: src/exceptions/OFException.m
==================================================================
--- src/exceptions/OFException.m
+++ src/exceptions/OFException.m
@@ -12,12 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include <stdlib.h>
 
 #ifdef HAVE_DLFCN_H

Index: src/of_asprintf.m
==================================================================
--- src/of_asprintf.m
+++ src/of_asprintf.m
@@ -12,12 +12,10 @@
  * Public License, either version 2 or 3, which can be found in the file
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>