Recent public discussion on Australian citizenship restricts to how aliens or children of aliens may acquire it, and whether government should have power to cease it on a discretionary decision. Less public is discussion on whether Parliament can define the rights and obligations of citizenship without power sourced from the Constitution. But the more serious problem overlooked for over 60 years is: Is citizenship at birth constitutionally –valid? Citizenship acquired at birth includes all born in Australia and born to an Australian parent. Prior to 1948, a natural-born British subject was determined by UK Parliament law. The Constitution did not duplicate a power to Australian Parliament to make similar laws and none has been granted since. The Australian Nationality and Citizenship Act 1948 introduced the Australian-born citizen at the same time the UK Parliament repealed laws determining nationality of those born in Australia. But Australian Parliament had no source of power to make law to determine conditions for acquisition or loss of nationality at birth. Parliament was limited to making laws on naturalization and aliens, and immigration and emigration, but none for citizenship at birth. It seems either the UK Parliament exceeded its power prior to 1948, or the Australian Parliament after. This affects every Australian born after 1948 in Australia or to an Australian parent. Australian citizenship relies on a faith in government to overlook the vulnerability that will remain until the Constitution is amended. But the way forward is treacherous. The Constitution does not prevent a future government deciding citizenship at birth is not valid and to call a referendum to make amends. The conundrum is the Constitution does not assure the Australian-born a right to vote and it may be an valid citizenship is reason to deny a vote. That leaves the fate of the Australian-born in the hands of a decision made only by naturalized Australians: not born in Australia and not to an Australian parent. Notably the most recently elected PMs are naturalized.