Pump cassettes, infusion systems, and methods are described. An example pump cassette may include a rigid body comprising a frame portion, a base portion, a compliant membrane disposed substantially therebetween, two opposing edge sections, and an interface-facing surface. The rigid body may include a positioning feature arranged substantially orthogonal to a general plane of the interface-facing surface. The pump cassette may include a slider coupled to the two opposing edge sections and longitudinally articulable with respect to the rigid body.