of the 2014–15 season, Klostermann was given a handful of first team appearances following the club's defensive crisis. He then scored his first goal for the club on 24 April 2015, in a 2–1 win over Darmstadt 98. At the end of the 2014–15 season, Klostermann went on to make a total of 15 appearances and scoring once in all competitions. In the 2015–16 season, Klostermann started the season, playing in the right–back position for the side and soon became the club's first choice throughout the season. He set up a goal for Davie Selke, in a 2–2 draw against Greuther Fürth on Matchday 2. He then scored his first goal of the season, in a 2–1 win over 1860 Munich on 13 March 2016. Klostermann later helped the club get promoted to the Bundesliga for the first time after beating Karlsruher SC 2–0 on 8 May 2016. Despite missing out three matches, due to injuries later in the 2015–16 season, Klostermann went on to make a total of 31 appearances and scoring once in all competitions. Ahead of the 2016–17 season, Klosterman was linked with a move away from RB Leipzig, as Premier League duo Tottenham Hotspur and Arsenal showed interest. However, his season was overshadowed with injuries. He only made one (and only) appearance this season, starting the whole game, in a 1–0 win over Borussia Dortmund on Matchday 2. While rehabilitating his injuries, Klostermann signed a contract extension with the club, keeping him until 2021. It wasn't until May 2017 when he returned to training with the first team on a full recovery. The 2017–18 season saw Klostermann regaining his first team place at RB Leipzig, playing in the right–back position. Despite his absence at the start of the season, he scored his first goal for the club, in a 2–1 win over 1. FC Köln on 1 October 2017. In the second half of the 2017–18 season, Klostermann lost his place in the right–back position to Konrad Laimer. Instead, he began to play in the left–back position for the rest of the 2017–18 season, although he occasionally played in the right–back position. At the end of the 2017–18 season, Klostermann went on to make thirty–nine appearances in all competitions. Ahead of the 2018–19 season, Klostermann was linked with a move to Serie A side A.S. Roma but dismissed the move and wanted to stay at the