Disproportionate costs of switching focal attention within working memory have been put forward as an explanation for age-related performance impairment on the n-back task. The lag (n) in the n-back task is confounded by memory load, however. In the current study, it was attempted to tackle this issue by introducing a two-digit 1-back condition. This condition was intended to bridge the gap between the conventional 1-back and 2-back conditions by increasing memory load, but not n. Twenty young (mean age=22 years) and 20 older adults (mean age=65 years) were subjected to this adapted n-back paradigm. The results corroborated earlier results in that, relative to the young participants, the older participants were disproportionately impaired in the 2-back condition relative to both the conventional one-digit and the two-digit 1-back conditions. In line with previous research, this interaction was only found in the accuracy scores, not in the reaction times. It was concluded that disproportionate costs of focus switching rather than memory load explain age-related impairment on the n-back task.