The two biggest public pension funds in the U.S. are performing better this year but the performance is not likely to last, according to an article in The Wall Street Journal.

The funds—the California State Teacher’s Retirement System (Calstrs) and California Public Employee’s Retirement System (Calpers)—which together manage $575 billion for 2.8 million public workers and retirees–have both earned more than 8% for the second fiscal year in a row, the article reports, “thanks to a robust performance by stocks and private equity.”

But the article explains that the funds are not counting on the performance continuing over the long term: “Both rolled back their investment targets this year in an effort to be more realistic about what they can earn in the future.” It adds that other public pensions around the country are also becoming more cautious about future earnings projections, with many reducing return assumptions to a maximum of 7%.

Steve Foresti, CIO of Wilshire Consulting, is quoted: “We probably want to temper our enthusiasm when we have a year or two year of strong returns because one thing we know for certain is that there will be challenging years.”

The article notes that moving expectations under 8% has “real-life consequences” since such predictions are used to calculate the present value of what’s owed to retirees. “Even slight cutbacks in return targets,” it says, “often mean budget-strained governments or workers are asked to pay significantly more to account for liabilities that are expected to rise as lifespans increase and more Americans retire.”