Secondary flows near the endwall of a turbine blade contribute to a loss in aerodynamic performance in the engine. Further reductions in performance occur when the secondary flows interact with leakage flow from necessary clearance features, such as the clearance gap between the blade rotor and an upstream stator or gaps between adjacent blade platforms. Non-axisymmetric endwall contouring has been shown to reduce the strength of secondary flows near the endwall, but relatively little research has been done to test the sensitivity of the contouring to the endwall leakage features. This paper describes aerodynamic measurements taken downstream of a cascade with representative leakage features. In general, upstream leakage flow with swirl relative to the blade increased aerodynamic loss, relative to leakage that was matched to the blade wheelspeed. Non-axisymmetric contouring for an endwall without a platform gap reduced underturning of the flow but had no effect on overall loss, relative to a flat endwall without a gap. A contoured endwall with a platform gap had 12% higher mixed-out loss than a contoured endwall without a gap.