diff --git a/unix/m4/uintmax_t.m4 b/unix/m4/uintmax_t.m4
new file mode 100644
index 0000000..bf83ed7
--- /dev/null
+++ b/unix/m4/uintmax_t.m4
@@ -0,0 +1,30 @@
+# uintmax_t.m4 serial 9
+dnl Copyright (C) 1997-2004 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 From Paul Eggert.
+
+AC_PREREQ(2.13)
+
+# Define uintmax_t to 'unsigned long' or 'unsigned long long'
+# if it is not already defined in <stdint.h> or <inttypes.h>.
+
+AC_DEFUN([gl_AC_TYPE_UINTMAX_T],
+[
+  AC_REQUIRE([gl_AC_HEADER_INTTYPES_H])
+  AC_REQUIRE([gl_AC_HEADER_STDINT_H])
+  if test $gl_cv_header_inttypes_h = no && test $gl_cv_header_stdint_h = no; then
+    AC_REQUIRE([gl_AC_TYPE_UNSIGNED_LONG_LONG])
+    test $ac_cv_type_unsigned_long_long = yes \
+      && ac_type='unsigned long long' \
+      || ac_type='unsigned long'
+    AC_DEFINE_UNQUOTED(uintmax_t, $ac_type,
+      [Define to unsigned long or unsigned long long
+       if <stdint.h> and <inttypes.h> don't define.])
+  else
+    AC_DEFINE(HAVE_UINTMAX_T, 1,
+      [Define if you have the 'uintmax_t' type in <stdint.h> or <inttypes.h>.])
+  fi
+])