diff --git a/unix/m4/ulonglong.m4 b/unix/m4/ulonglong.m4
new file mode 100644
index 0000000..dee10cc
--- /dev/null
+++ b/unix/m4/ulonglong.m4
@@ -0,0 +1,23 @@
+# ulonglong.m4 serial 4
+dnl Copyright (C) 1999-2004 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.
+
+# Define HAVE_UNSIGNED_LONG_LONG if 'unsigned long long' works.
+
+AC_DEFUN([gl_AC_TYPE_UNSIGNED_LONG_LONG],
+[
+  AC_CACHE_CHECK([for unsigned long long], ac_cv_type_unsigned_long_long,
+  [AC_TRY_LINK([unsigned long long ull = 1ULL; int i = 63;],
+    [unsigned long long ullmax = (unsigned long long) -1;
+     return ull << i | ull >> i | ullmax / ull | ullmax % ull;],
+    ac_cv_type_unsigned_long_long=yes,
+    ac_cv_type_unsigned_long_long=no)])
+  if test $ac_cv_type_unsigned_long_long = yes; then
+    AC_DEFINE(HAVE_UNSIGNED_LONG_LONG, 1,
+      [Define if you have the 'unsigned long long' type.])
+  fi
+])