Klitschko, the holder of the WBA, WBO and IBF straps, will take on the American-based Wach in Hamburg, Germany.
The 36-year-old has beaten virtually every heavyweight contender out there and defeated Tony Thompson for a second time in his latest defence last month.
Wach should present little threat having fought only journeymen in a 27-0 career, although for once Klitschko will take on the taller man at 6ft 7in.
"It is always something special to box in Hamburg," said Klitschko.
"This fight will also be special because I have never fought against a boxer who is bigger than me and has a longer reach."