[plt-scheme] loading extension in a module

Hi, I'm learning how to write a C extension.  The files are here:

http://primate.net/~itz/plt-posix/

The problem I'm running into is as follows:

Welcome to MzScheme version 208, Copyright (c) 2004 PLT Scheme, Inc.
> (load-extension "plt_stat.so")
> c-lstat
#<primitive:c-lstat>
> (c-lstat "plt_stat.so")
0
771
0
0
6308513
0
0
509
0
0
8
0
0
1
0
0
1000
0
0
1000
0
0
0
0
0
38673
0
0
28000149
1
0
28000077
1
0
28000077
1
0
> (require "stat.ss")
stat.ss:64:42: compile: unbound variable in module in: c-lstat
> 

What am I doing wrong?  TIA

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