Mainz and Adam Szalai have agreed on a contract extension.
"Adam is a pillar in the team and played a big part in the outstanding second half of the past season," said Mainz boss Christian Heidel.
"On the pitch, he is an absolute fighter and an unpleasant opponent for any defender, always leading the way for his team.
"And in the dressing room, Adam is an important integration figure that the young players in particular can look up to."
Szalai scored two goals in 20 games last season.