Same thing as always. Stick with your plan and rebalance if you need to. If your plan is 80% stock 20% bond (or whatever ratios), and the increased stock prices are putting you significantly out of balance, then sell your stock funds and buy bonds to put it back to where it should be. If the crash happens, sell your now too-high bonds and buy stocks. Or just buy into one of those funds that does all this for you, or hire a fiduciary financial advisor to do it for you.