The national side have struggled at the back in recent international friendlies, with nine goals having been let in during just three matches.
Mertesacker, however, said that the players are working hard on their defensive shape and how it comes together as a system.
"We discussed the basic principles of our defensive play, concerning the back four in particular," he told Dfb.de.
"I think it was a good idea, especially after the game against Paraguay and because we hadn't got together for a while. Basically we just went over the defensive philosophy of the national team.
"[We discussed] when should we drop deep? When should we press forward? What should we do in one-on-one situations? How can we cover one another better? What should we do in certain situations?"
The game kicks off at the Allianz Arena at 7.45pm.