I used 0. Didn't work.

Probably because your protoype is wrong.

This: my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LLLLLL', 'L')

Should be this: my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LPLPPP', 'L')

Fix that, and your 'fix' above is unnecessary.

Just another hack at a module that worked fine for the most part before people start trying 'fix it' without enough knowledge to do so.

I wouldn't call it excitement. More depression when I see people proffering this kind unnecessary complexity:

sub get_pv { local $^W; unpack 'L!', pack 'P', $_[0] }

BEGIN {
   # BOOL PeekNamedPipe(
   #    HANDLE  hNamedPipe,
   #    LPVOID  lpBuffer,
   #    DWORD   nBufferSize,
   #    LPDWORD lpBytesRead,
   #    LPDWORD lpTotalBytesAvail,
   #    LPDWORD lpBytesLeftThisMessage
   # )

   my $f = Win32::API->new('kernel32', 'PeekNamedPipe', 'LLLLLL', 'L')
      or die $^E;

   sub PeekNamedPipe {
      my $nBytesRead;
      my $nTotalBytesAvail;
      my $nBytesLeftThisMessage;

      $nBytesRead            = pack('L!', $_[3]) if defined $_[3];
      $nTotalBytesAvail      = pack('L!', $_[4]) if defined $_[4];
      $nBytesLeftThisMessage = pack('L!', $_[5]) if defined $_[5];

      my $rv = $f->Call(
         $_[0],
         get_pv($_[1]),
         $_[2],
         get_pv($nBytesRead),
         get_pv($nTotalBytesAvail),
         get_pv($nBytesLeftThisMessage),
      );

      $_[3] = unpack('L!', $nBytesRead           ) if defined $_[3];
      $_[4] = unpack('L!', $nTotalBytesAvail     ) if defined $_[4];
      $_[5] = unpack('L!', $nBytesLeftThisMessage) if defined $_[5];

      return $rv;
   }
}
[download]

for the sake of a little reading, and a couple of zeros. The icing on the cake is when they try to claim the technical high ground as justifiction for it.