A super-frame for transmission in an optical communications system comprises two or more data frames and a parity frame. All frames in the super-frame have been encoded in accordance with a first Forward Error Correction (FEC) scheme. The parity frame is computed over the two or more data frames (prior to or concurrently with or after encoding via the first FEC scheme) according to a second FEC scheme. At a receiver, the super-frame is decoded in accordance with the first FEC scheme to generate a set of FEC decoded frames in which residual errors are clustered, that is, are non-Poisson. The second FEC scheme, which is particularly suited or designed to correct the clustered non-Poisson residual errors, is used to correct the residual errors.