Storage circuitry is provided with increased resilience to single event upsets, along with a method of operation of such circuitry. The storage circuitry has a first storage block configured in at least one mode of operation to perform a first storage function, and a second storage block configured in at least one mode of operation to perform a second storage function distinct from said first storage function. Configuration circuitry is responsive to a predetermined mode of operation where the second storage function is unused, to configure the second storage block to operate in parallel with the first storage block. By arranging the two storage blocks in parallel when one of the storage blocks is otherwise performing no useful function, this in effect increases the size of the storage block that is still performing the useful storage function, and as a result increases its resilience to single event upsets. Such an approach has minimal area and power consumption overhead, and provides a small storage circuit that can be readily used in a wide variety of sequential cell designs.