-AC_DEFUN([gl_USE_SYSTEM_EXTENSIONS],
- [AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])])
+AC_DEFUN_ONCE([gl_USE_SYSTEM_EXTENSIONS],
+[
+ dnl Require this macro before AC_USE_SYSTEM_EXTENSIONS.
+ dnl gnulib does not need it. But if it gets required by third-party macros
+ dnl after AC_USE_SYSTEM_EXTENSIONS is required, autoconf 2.62..2.63 emit a
+ dnl warning: "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
+ dnl Note: We can do this only for one of the macros AC_AIX, AC_GNU_SOURCE,
+ dnl AC_MINIX. If people still use AC_AIX or AC_MINIX, they are out of luck.
+ AC_REQUIRE([AC_GNU_SOURCE])
+
+ AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+])