Negative yStride

I'm reading into an image buffer where the lines are ordered from bottom to top, so I'm using a negative yStride like so:

frameBuffer.insert(name,
                    Slice(Imf::FLOAT,
                            last_line_ptr,
                            xStride,
                            -rowbytes, // yStride
                            xSampling, ySampling, fill) );


But one thing I noticed is that Slice's yStride is a size_t, which is unsigned.  So instead of a modest negative number, the debugger shows it as a huge unsigned integer.

It seems to work fine, but I find it a little off-putting.  Should I be worried?


Brendan