Having already promised a five-card suit, your next call should send more information about your hand. The most descriptive call is four no-trump.
Partner can now evaluate the combined strength accurately to reach the best partnership decision.
Q. Partner opens one spade, and next hand overcalls one no-trump. If you held enough high-card strength to force another bid from partner, you would have doubled RHO for penalties. If your long suit is a major, it's probably a good idea to open in the major. If your long suit is a minor, it will ease a rebidding problem if you choose to open one no-trump. However, if both doubletons are very weak, I do not recommend opening one no-trump.