One of the biggest winners in the push to make money-market funds safer for investors is turning out to be none other than the U.S. government.

Rules adopted by regulators last month will require money funds that invest in riskier assets to abandon their traditional $1 share-price floor and disclose daily changes in value. For companies that use the funds like bank accounts, the prospect of prices falling below $1 may prompt them to shift their cash into the shortest-term Treasuries, creating as much as $500 billion of demand in two years, according to Bank of America Corp.

Boeing Co., the world's largest maker of planes, and the state of Maryland are already looking to make the switch to avoid the possibility of any potential losses. With the $1.39 trillion U.S. bill market accounting for the smallest share of Treasuries in six decades, the extra demand may help the world's largest debtor nation contain its own funding costs as the Federal Reserve moves to raise interest rates.