Ada-mode: Character constant not highlighted

[Erik]

See the following code:
procedure Prov is
   C : constant Character := ' ';
begin
   case C is
      when ' ' | 'n' | ''' | 'm' =>
         null;
      when others                =>
         null;
   end case;
end Prov;


Emacs 22.1.1 (Gentoo package app-editors/emacs-22.1-r3) does not
highlight ''' like the other character constants.