In 1970, West Germany recognised the Oder-Neisse line as the de facto western boundary of Poland by the Treaty of Warsaw; and in 1973, the Federal Constitutional Court acknowledged the capability of East Germany to negotiate the Treaty of Zgorzelec as an international agreement binding as a legal definition of its boundaries. In signing the Helsinki Final Act in 1975, both West Germany and East Germany recognised the existing boundaries of post-war Europe, including the Oder-Neisse line, as valid in international law.