Euh... this is the incorrect fix. The 0 is wrong to begin with.
Mark Favas submitted a proper patch for this. See his "Revised Patches for bug report 258" posted to patches@python.org on April 4th.
Sigh. You're right. I've seen two patches to mmapmodule.c since he posted that patch, and no comments on his patch, so I thought his patch was already incorporated. I was wrong. Note that this module still gives 6 warnings on VC6.0, all C4018: '>' or '>=' signed/unsigned mismatch. I wish someone gave me a patch for that too. Unrelated: _sre.c also has a bunch of VC6 warnings -- all C4761, integral size mismatch in argument: conversion supplied. This is all about the calls to SRE_IS_DIGIT and SRE_IS_SPACE. The error occurs 8 times on 4 different lines, and is reported in a cyclic fashion: 106, 108, 110, 112, 106, 108, ..., etc., probably due to sre's recursive self-include tricks? --Guido van Rossum (home page: http://www.python.org/~guido/)