--- a/m4/gnu-source.m4
+++ b/m4/gnu-source.m4
@@ -1,25 +1,12 @@
-#serial 3
-# Make sure _GNU_SOURCE is defined where necessary: as early as possible
-# for configure-time tests, as well as for every source file that includes
-# config.h.
-
-# From Jim Meyering.
-
-AC_DEFUN([AC__GNU_SOURCE],
-[
-  # Make sure that _GNU_SOURCE is defined for all subsequent
-  # configure-time compile tests.
-  # This definition must be emitted (into confdefs.h) before any
-  # test that involves compilation.
-  cat >>confdefs.h <<\EOF
+# AC_GNU_SOURCE
+# --------------
+AC_DEFUN([AC_GNU_SOURCE],
+[AH_VERBATIM([_GNU_SOURCE],
+[/* Enable GNU extensions on systems that have them.  */
 #ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif
-EOF
-
-  # Emit this code into config.h.in.
-  # The ifndef is to avoid redefinition warnings.
-  AH_VERBATIM([_GNU_SOURCE], [#ifndef _GNU_SOURCE
-# define _GNU_SOURCE
-#endif])
+# undef _GNU_SOURCE
+#endif])dnl
+AC_BEFORE([$0], [AC_COMPILE_IFELSE])dnl
+AC_BEFORE([$0], [AC_RUN_IFELSE])dnl
+AC_DEFINE([_GNU_SOURCE])
 ])