Kylie Jenner has not changed her tune on Tyga ... not only is she still with him, she has her sights set on marriage.

Kylie was leaving some sort of studio in L.A. Monday night, when the photog asked the marriage question for the second time. You may recall, a few months back another photog asked the same question and Kylie said she would take a walk down the aisle with Tyga.

It seemed on the surface the relationship had cooled, but unless she's screwing with everyone, this 18-year-old has made her decision.

And considering this photo Kylie posted ... Tyga might wanna lock that down ASAP.