20 CFR §216.65

1. (a)Was married to the employee for at least 9 months before the day the employee died;
2. (b)Is the natural parent of the employee's child;
3. (c)Was married to the employee when either the employee or the widow(er) adopted the other's child, or they both legally adopted a child who was then under 18 years old;
4. (d)Was married to the employee less than 9 months before the employee died but, at the time of marriage, the employee was reasonably expected to live for 9 months; and
   1. (1)The employee's death was accidental;
   2. (2)The employee died in the line of duty while he or she was serving active duty as a member of armed forces of the United States; or
   3. (3)The surviving spouse was previously married to the employee for at least 9 months;
5. (e)Was entitled in the month before the month of marriage to either:
   1. (1)A benefit under section 202 of the Social Security Act as a widow, widower, spouse (divorced spouse, surviving divorced spouse), father, mother, parent, or disabled child; or
   2. (2)An annuity under the Railroad Retirement Act as a widow, widower, divorced spouse, or surviving divorced spouse, parent or disabled child; or
6. (f)Could have been entitled to a benefit listed in paragraph (e) of this section, if the widow(er) had applied and been old enough to qualify therefor in the month before the month of marriage.