A rotary lawn mower of the type having a circular housing with adjustably mounted ground engaging wheels. A side shield is provided in the form of a vertical plate of metal arranged fore-and-aft between the wheels and closely alongside the housing. The shield is supported at its ends on the front and rear axles, extending close to the ground to prevent ejection of a missile at ground level and of sufficient height to prevent discharge at a higher level in all positions of housing adjustment. Preferably the housing has a laterally extending horizontal apron along its lower edge while the side shield has a pair of inwardly extending tabs along its upper edge in overlapping relation to the ends of the apron to prevent ejection of a missile upwardly in the space adjacent the wheel treads. As an alternate construction, the shield has an inwardly extending ledge which conforms to the wall of the mower housing.