5 C.F.R. § 839.401

What can I elect if I was put in CSRS or CSRS Offset by mistake?

If you were placed in CSRS or CSRS Offset due to a qualifying retirement coverage error and you should have been in FERS, you may elect CSRS Offset or FERS. If you were placed in CSRS or CSRS Offset due to a qualifying retirement coverage error and you should have been in Social Security-Only, you may elect CSRS Offset or Social Security-Only. This is summarized in the following chart:

You are in: | And you belong in: | You may elect:; CSRS | FERS | CSRS Offset or FERS.; CSRS Offset | FERS; CSRS | Social Security-Only | CSRS Offset or Social Security-Only.; CSRS Offset | Social Security-Only