Sometimes yes, sometimes no. I have two SOS's -- the 871 is prone to roll before the park engages, and the 4000 less so. Try a couple of tricks that have been mentioned here -- hold down the inching pedal, shift to 10th and then quickly to park. Some say to do the same thing from 5th. One thing's for sure -- you ought not ever trust that it's engaged until you verify, like on a hill. Othersiwise, shut it off before dismounting, then the will lock up for sure.