If an individual does not have a tax home (as defined in section 911(d)(3)), the residence of such individual shall be the United States if such individual is a United States citizen or a resident alien and shall be a country other than the United States if such individual is not a United States citizen or resident alien. If the taxpayer is a U.S. person and has no principal place of business outside the United States, the residence of the taxpayer is the United States. Notwithstanding paragraph (d)(1)(ii) of this section, if a partnership is formed or availed of to avoid tax by altering the source of exchange gain or loss, the source of such gain or loss shall be determined by reference to the residence of the partners rather than the partnership.
26 C.F.R. §1.988-4