ThreadLocal and constness

I'm trying to use the Support/ThreadLocal class, and I'm having some trouble because ThreadLocalImpl::getInstance returns a const void*, which I would like to be able to modify. Is there any particular reason this returns a const pointer rather than simply a void pointer? Pthreads and the Windows TLS API both seem to return plain void*.

If there's no particular reason for this, could this be patched to not be const?

Thanks,
Stephen