With the Oakmark International Small Cap Fund topping $325 million in assets, the fund's investment advisor, Harris Associates, closed the fund to new investors last week. Existing shareholders, however, may continue to purchase additional shares and reinvest dividends and capital gains.

"We are closing the fund to new investors as a result of strong performance and stock cash inflows," said David Herro, co-portfolio manager of the fund along with Michael Welsh. Year to date through May 3, the fund has returned 15.5%, and for the one year trailing, the fund is up 20.7%, according to Morningstar. By comparison, the S&P 500 is down 6.2% for the same period year to date, and down 12.9% for the one year trailing, according to Morningstar.

"Limiting asset growth allows us to maintain investment flexibility and to remain true to the fund's mandate, [which is] to invest in small-cap companies based outside of the U.S.," Herro said. "We've closed other funds in our family before, always with our shareholders' best interests in mind," he added.

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