Disclosed is a device for preventing gases from escaping when coal cakes (15) are fed into horizontal coking chambers (20), the coal cakes being produced outside the coking chamber (20) in a mould by a tamping, feed and pusher machine (1) and standing on the movable floor (14) of the mould. The device is designed as a channel (3) which surrounds the coal bakes (15) being fed in. The channel end wall nearest the oven abuts the frame (2) of the coking-chamber door. The device is characterized by the fact that the side walls (10) of the channel (3) can be inserted into the side walls of the mould which are hollow in the zone nearest the oven. In addition, the channel floor is formed by the movable floor (14) of the mould and the channel roof (9) is telescopic and has guides for the movable side walls (10). Located on the stationary part of the channel roof (9) is a levelling device (8) which levels the surface of the coal cake (15) and has a disposal device for the coal thus stripped off.