Timepiece date mechanism

A timepiece date mechanism comprising a units indicator runner equipped with ten teeth or with a multiple of ten teeth and a tens indicator runner equipped with four teeth or with a multiple of four teeth, a transmission connecting the units and tens indicator runners to move the latter runner on by one step for every ten steps of the units indicator runner and a drive runner for driving the units indicator runner, connected to the indicator geartrain of the timepiece, wherein one tooth of the units indicator runner for moving on from “1” to “2” is a tooth of an auxiliary runner the rotation spindle of which is secured to the units indicator runner and is able to engage alternately with the teeth of the tens indicator runner and with a cam coaxial with and secured to this tens indicator runner, this cam comprising, on the one hand, at least one part for angularly immobilizing said auxiliary runner and, on the other hand, at least one cut-out the position of which is chosen to allow said auxiliary runner to drive said tens indicator runner by one step between “31” and “01” without driving the units indicator runner.