An arrangement for gasifying solid fuel includes a gasification reactor for producing further oxidizable product gas from solid fuel and a gas treatment reactor arranged in a flow direction of the product gas in gas flow connection with the gasification reactor. The gas treatment reactor includes a supply for supplying oxygenous gas to the gas treatment reactor for partial oxidization of product gas and for thermal cracking thereof. A radiation heat exchange cooler for cooling the product gas is arranged in connection with the gas treatment reactor to solidify melt components in the product gas. A discharge connection is arranged in the lower portion of the radiation heat exchange cooler for removing solidified melt components from the radiation heat exchange cooler. A method of gasifying solid fuel in a gasification reactor is also presented.