(a) Except as provided in §§ 843.307 and 843.312, and paragraph (b) of this section, if an annuitant dies and is survived by a current spouse, the current spouse is entitled to a current spouse annuity equal to 50 percent of an annuity computed under subpart D of part 842 of this chapter, with respect to the retiree, unless—

(1) The right to a current spouse annuity was waived under § 842.603 of this chapter (and no election was subsequently made under § 842.610 of this chapter nullifying the waiver); or

(2) In the case of a marriage after retirement, the retiree did not file an election under § 842.612 of this chapter.

(b) A current spouse who married the retiree after retirement is entitled to an annuity under paragraph (a) of this section only upon electing this annuity instead of any other survivor benefit to which such spouse may be entitled under this subpart, subpart B of this part, or under another retirement system for Government employees.