Mo. Rev. Stat. § 578.530
It shall be an affirmative defense to prosecution for a violation of sections 578.520 and 578.525 that the premises were at the time open to members of the public and the person complied with all lawful conditions imposed concerning access to or the privilege of remaining on the premises.
(L. 2007 S.B. 198)
*This section was repealed by S.B. 491, 2014, effective 1-01-17. Due to the delayed repeal date, the version of this section in effect until 12-31-16 is printed here.