MacKinnon introduced the interesting concept of an idiot-proof tile. This is a polyomino-shaped tile P which has the property that wherever two copies are placed (“by an idiot”) on the square grid, then—so long as the copies do not overlap or enclose a region (“even an idiot would not do that”)—it is possible to adjoin further copies of P so as to complete a tiling of the whole plane. MacKinnon proved that the L-triomino is an idiot-proof tile, and indicated how one could prove that the W-pentomino has the same property. The purpose of this note is to extend MacKinnon’s results, and to formulate some open problems.