A method of operating a memory device comprises receiving a first row address corresponding to a first word line in the first sub bank array and corresponding to a first word line in the second sub bank array, determining whether at least one of the first word lines has been replaced with a spare word line, (a) when neither of the first word lines has been replaced, receiving a first number of row addresses for refresh operations in order to refresh adjacent word lines to the first word lines, and (b) when at least one of the first word lines has been replaced with a spare word line, receiving a second number of row addresses for refresh operations in order to refresh adjacent word lines to any non-replaced first word and any spare word lines, wherein the second number is greater than the first number.