This paper describes the design and construction of the unique widening of a concrete arch bridge over the River Ohře using a lightweight steel superstructure. The bridge reconstruction formed part of the wider reconstruction measures for road I/6, including its upgrade from a two- to a four-lane highway, near Loket between Nové Sedlo and Sokolov in the north-west of the Czech Republic. Details of the erection of the steel structure and the strengthening of the concrete arch and piers are also given.