The pair are united again with the France squad this week. Mandanda is back after quitting Palace for Marseille.
Koscielny said, "He is a very great goalkeeper. I think that his return to Marseille did him good.
"His year at Crystal Palace showed him that in football nothing is ever guaranteed. He's a golden guy, I like him a lot.
"He is always there to work and give the best for the team."