Your file size is a somewhat larger integer than the usual 32-bit integer can hold. Perl can actually go a few bits larger using the wider float type, but I don't think that's quite enough.

The problem might extend to the C library's stat() call.

Try running you program on a perl built for 64-bit integers (which can be done on any platform). If it's still broken, look to the C libs.

If the size reporting is not that critical, you can just say something like,  printf 'Size: %s', $size < 0 ? '> 2 GB' : $size;</code>