[plt-scheme] question about "module: initial import not well formed"

I am trying to open a module with a minimal number 
of bindings, and reading "The require-spec must be 
as for require" at:

  http://docs.plt-scheme.org/reference/module.html

had thought that:

  (module x (only-in scheme/base define ...)
  ...)

should work?  However I get 

> Welcome to MzScheme v3.99.0.17 [3m], Copyright (c) 2004-2008 PLT Scheme Inc.
> x.ss:1:12: module: initial import is not a well-formed module path at: (only-in scheme/base define ...

What should i be writing?

Thanks,
Rohan

PS. i think "where require is the preimitive 
require form" in the same paragraph means to 
say "primitive"