A reactor (1) for preparing phosgene by gas-phase reaction of carbon monoxide and chlorine in the presence of a solid catalyst, which reactor has a bundle of parallel catalyst tubes (2) aligned in the longitudinal direction of the reactor whose ends are fixed in tube plates (3) and have a cap (4) at each end of the reactor (1), and has deflection plates (6) which are aligned perpendicular to the longitudinal direction of the reactor in the intermediate space (5) between the catalyst tubes (2) and leave free passages (7) located alternately opposite one another on the interior wall of the reactor, and in which the catalyst tubes (2) are charged with the solid catalyst, the gaseous reaction mixture is passed from one end of the reactor via one cap (4) through the catalyst tubes (2) and is taken off from the opposite end of the reactor (1) via the second cap (4) and a liquid heat transfer medium is passed through the intermediate space (5) around the catalyst tubes (2), where the reactor (1) has no tubes in the region of the passages (7), is proposed.