A crushing device includes a horizontal shaft impact crusher having an impeller rotating around a horizontal shaft and at least one curtain against which material may be crushed. The crushing device further includes a first feeding device for feeding a first type of material to be crushed to a crushing chamber of the horizontal shaft impact crusher. A second feeding device feeds a second type of material, having a smaller average particle size than the first type of material, to the crushing chamber simultaneously with the first feeding device feeding the first type of material to the crushing chamber. A mixing arrangement for at least partially mixes the first and the second types of materials with each other before bringing them into contact with the impeller.