[fpc-pascal] Code works on Linux x64 but not on Linux x86

[Reinier Olislagers]

I have the following code, adapted from pasbzip.pas (bzip2 example)
uses ...bzip2..

const
  BufferSize = 4096;
var
  infile, outfile: Tbufstream;
  decoder: Tbzip2_decode_stream;
  a: array[1..BufferSize] of byte;
  readsize: cardinal;
  Status: boolean;
begin
  Status := False;
  result:=false;
...
  try
    infile.init(SourceFile, stopenread, 4096);
    outfile.init(TargetFile, stcreate, 4096);
    decoder.init(@infile);
    if decoder.status <> stok then
    begin
...
      repeat
        readsize := BufferSize;
        decoder.Read(a, readsize);
        Dec(readsize, decoder.short);
        outfile.Write(a, readsize);
      until decoder.status <> 0;
    end;
    infile.done;
    outfile.done;
...

Code bombs at decoder.Read(a, readsize). readsize=0 according to debugger.
readsize=cardinal; according to help "an unsigned 32-bit integer".
However,
http://wiki.lazarus.freepascal.org/Multiplatform_Programming_Guide#32.2F64_bit
seems to imply Cardinal can vary between 32 bit and 64 bit.

Is that the culprit or am I doing anyth else wrong?

Thanks,
Reinier