Vytautas's distrust of Polish sovereignty over Lithuania may have been well founded, since Władysław had in principle signed Lithuania's independence away in 1385 in the formal act of union, by which he agreed to incorporate Lithuania into Poland. The Union of Vilnius and Radom of 1401 reaffirmed Vytautas's tenure as grand duke under Władysław's overlordship, but it assured the title of grand duke to Władysław's heirs rather than to those of Vytautas: if Władysław died without heirs, the Lithuanian boyars were to elect a new monarch. Since neither Władysław nor Vytautas had yet produced an heir, the implications of the act were unforeseeable.