Why is turbo tax defining the contribution limit to a SEP IRA as $6500 ? in the past it was calulated as a maximum 20% of self employed income

My wife is self employed, age 57, and contributed $24,000 to her SEP IRA in 2017 that was full adjusted for the AGI. Using Turbo Tax for 2018, it says her limit is $6500. What changed in the tax code OR is Turbo Tax not treating SEP IRA's properly now.