He scored his first goal for the club in a 1 -- 1 draw with Arminia Bielefeld .
In May 2017 , Union Berlin announced the signing of Hartel on a three - year deal .
Hartel scored Hartel 's first goal for the club in a 1 -- 1 draw with Arminia Bielefeld .
In May 2017 , Union Berlin announced the signing of Hartel on a three - year deal .