It is widely accepted that knowledge is incompatible with the presence of non-neutralized defeaters. A common way of addressing this issue is to introduce a condition to the effect that there are no non-neutralized defeaters for the belief that _p_ (i.e. a “no-defeaters condition”). I argue that meeting this condition leaves open a possibility for defeaters to squander our knowledge. The no-defeaters condition can be fortuitously met, and as a result it can be met luckily. I shall argue that this (...) kind of luck is inconsistent with knowledge. In order to prevent this pernicious form of luck I introduce a “defeaters-responsiveness” condition, according to which subjects ought to be disposed to adequately address defeaters if they were to arise (even if they in fact do not arise). (shrink)