Mo. Rev. Stat. § 115.265
If any electronic voting machine at a polling place becomes inoperative, the election judges shall immediately notify the election authority. If possible, the election authority shall repair or replace the machine. If an electronic voting machine is replaced with another machine, the votes on both machines shall be recorded at the close of the polls and shall be added together in determining the results of the election. If the inoperative machine cannot be repaired, and no other machine is available for use, paper ballots made as nearly as practicable to the official ballot may be used. At the close of the polls, the votes on paper ballots and the votes on the electronic voting machines shall be recorded and shall be added together in determining the results of the election. All paper ballots used pursuant to this section shall be used in accordance with the laws affecting paper ballots and shall be returned to the election authority as paper ballots are returned with a statement describing how and why the paper ballots were voted.
§ 115.265, RSMo
Effective 1-1-78