John C. Bogle, the founder of Vanguard Group Inc. who popularized index-based investing, said proposed rules for money-market mutual funds don’t go far enough to protect investors and the financial system.

The U.S Securities and Exchange Commission’s June 5 proposal to make only the riskiest money funds, known as prime funds, adopt a floating share price is a “compromise” forced by the fund industry’s resistance to reform, Bogle said last week in remarks at the Morningstar Investment Conference in Chicago. Regulators should force all money funds to float their share price, he said.

“The fact is money-market fund net-asset values fluctuate and they don’t want to let the world know,” Bogle said, referring to fund-company executives.

Bogle, 84, has spent his career advocating for lower costs and investor-friendly practices in the financial industry, sometimes putting him at odds with the firm he founded in 1975. Vanguard was among a group of firms including Fidelity Investments and Charles Schwab Corp. that earlier this year urged regulators to exempt retail-oriented money funds from regulation and focus only on those prime funds that cater to institutional clients.

U.S. regulators have debated how to make money funds safer since the September 2008 collapse of the $62.5 billion Reserve Primary Fund. Former SEC Chairman Mary Schapiro championed a plan in late 2011 and 2012 that envisioned changing the accounting standard for all money funds, including those that invest only in government securities or municipal bonds. After running into opposition from the fund industry, the SEC, now led by Mary Jo White, approved a set of narrower proposals.