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diff --git a/gl/m4/extensions-aix.m4 b/gl/m4/extensions-aix.m4
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+++ b/gl/m4/extensions-aix.m4
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+# extensions-aix.m4
+# serial 1
+dnl Copyright (C) 2024-2025 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+
+# On AIX, most extensions are already enabled through the _ALL_SOURCE macro,
+# defined by gl_USE_SYSTEM_EXTENSIONS.  gl_USE_AIX_EXTENSIONS additionally
+# activates more GNU and Linux-like behaviours, affecting
+#   - the time_t type,
+#   - errno values in <errno.h>: ENOTEMPTY
+#   - functions in <stdlib.h>: malloc calloc realloc valloc
+#     <https://www.ibm.com/docs/en/aix/7.3?topic=m-malloc-free-realloc-calloc-mallopt-mallinfo-mallinfo-heap-alloca-valloc-posix-memalign-subroutine>
+#   - functions in <string.h>: strerror_r (returns 'char *', like glibc)
+#   - functions in <dirent.h>: scandir, alphasort, readdir_r
+#   - functions in <netdb.h>: gethostbyname_r gethostbyaddr_r
+#   - declarations in <unistd.h>: sbrk
+# and a couple of secondary <sys/*> header files.
+
+AC_DEFUN_ONCE([gl_USE_AIX_EXTENSIONS],
+[
+  AC_DEFINE([_LINUX_SOURCE_COMPAT], [1],
+    [Define so that AIX headers are more compatible with GNU/Linux.])
+])