Building nds2-client from master presents lots of inconsistent-missing-override warnings

When building the nds2-client package from master (fa50e349) I am presented with lots of (~100) warnings like this:

/Users/duncan/git/nds2-client/src/libndscxx/module/nds_gap_handler.hh:104:13: warning:
      'fill_gap' overrides a member function but is not marked 'override'
      [-Winconsistent-missing-override]
            fill_gap( buffer&           cur_buffer,
            ^

It would be great to get these resolved, but I have no ida what they mean so I can't offer any help. Apologies if there's already a ticket open for this.