The amendment makes it a class B misdemeanor to "knowingly or recklessly create, receive, exchange, send or possess" sexual images and text, even if that material is of the minor possessing it.
Sexting made headlines earlier this year when a prosecutor threatened to charge three teenage girls with child pornography when they took photos of themselves in their bras and some of those images ended up on their classmates' cell phones.
The amendment now goes to the Missouri House where it must be passed before the end of the legislative session on Friday.