diff --git a/unix/m4/longlong.m4 b/unix/m4/longlong.m4
new file mode 100644
index 0000000..7b399e0
--- /dev/null
+++ b/unix/m4/longlong.m4
@@ -0,0 +1,23 @@
+# longlong.m4 serial 5
+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_LONG_LONG if 'long long' works.
+
+AC_DEFUN([gl_AC_TYPE_LONG_LONG],
+[
+  AC_CACHE_CHECK([for long long], ac_cv_type_long_long,
+  [AC_TRY_LINK([long long ll = 1LL; int i = 63;],
+    [long long llmax = (long long) -1;
+     return ll << i | ll >> i | llmax / ll | llmax % ll;],
+    ac_cv_type_long_long=yes,
+    ac_cv_type_long_long=no)])
+  if test $ac_cv_type_long_long = yes; then
+    AC_DEFINE(HAVE_LONG_LONG, 1,
+      [Define if you have the 'long long' type.])
+  fi
+])