Democratic presidential candidate Pete Buttigieg says he wants to shore up Social Security by boosting the amount of annual wages subject to a payroll tax that funds the program.

Senator Bernie Sanders and other Democratic hopefuls have also said they would raise the tax that funds Social Security, but Buttigieg’s proposal takes a more moderate approach.

Buttigieg, the mayor of South Bend, Indiana, said he would raise the maximum annual earnings currently subject to the Social Security payroll tax to $250,000 from $132,900 to help extend the viability of the program. Workers and employees pay a combined 12.4% tax on their earnings -- 6.2% each -- up to a caped amount. That cap is raised annually under a formula linked to the average national wage, but rising income inequality has eroded the tax base.

“That would go a long way toward sustainability on the Social Security side,” Buttigieg said Saturday at an Iowa forum hosted by the AARP. Americans ages 65 and older are expected to comprise about 23% of the electorate in 2020 -- their largest share since at least 1970, according to The Pew Research Center.

Sanders in February proposed a boost in the income cap, but a larger one than what Buttigieg is endorsing. The Vermont senator introduced legislation that would continue to apply the 12.4% tax on earnings up to the current limit, but then also impose the levy on all income above $250,000. Three other Senate Democrats who are running for president co-sponsored his bill: Cory Booker of New Jersey, Kirsten Gillibrand of New York and Kamala Harris of California.