Would it be better to avoid the native size_t type and use a fixed size wasi_size_t?

For example in the following API signature:

uvwasi_errno_t uvwasi_fd_write(uvwasi_t* uvwasi,                                                                              
                               uvwasi_fd_t fd,                                      
                               const uvwasi_ciovec_t* iovs,                      
                               size_t iovs_len,                                  
                               size_t* nwritten);   

In this case it would make sense to pass the actual address of the nwritten out param in the wasm memory. However since wasi's size_t is fixed at 4 bytes, we wouldn't want to write a 64-bit value into that location. It seems that on LP64 systems we uvwasi_fd_write would currently write 8 bytes. Maybe I'm misunderstanding?