A vacuum cleaner comprises a removable dust separator. The dust separator has an inlet duct and an outlet duct. The inlet duct is arranged for fluid connection to a dirt-air duct on the cleaner, and the outlet duct is arranged for fluid connection to a motor intake duct on the cleaner. In accordance with the invention, the inlet duct and outlet duct share a common wall which divides the open ends of the ducts, an inlet duct sealing member is provided for forming an air-seal between the inlet duct and the dirty-air duct, and an outlet duct sealing member is provided for forming an air seal between the outlet duct and the motor intake duct. Both seals are thus required to fail in order to short-circuit the two dirty-air duct and the motor intake duct, despite there being a common wall section between the inlet duct and the outlet ducts.