A briefly presented target can be rendered invisible by a lingering sparse mask that does not even touch it. This form of visual backward masking, called object substitution masking, is thought to occur at the object level of processing. However, it remains unclear whether object-level interference alone produces substitution masking because previous studies manipulated only the presence or absence of a physical masking stimulus after the removal of the target, leaving the possibility of some image-level interference contributing to the total masking. To assess object-level interference in the present study, we used an illusory-contour figure as an object mask, adjacent to the possible target locations, which was created by rotating 4 previewed inducers shaped like Pac-Man to face inward to form a subjective square region. The illusory object persisting beyond the target offset reduced the visibility of the target only when presented in its immediate vicinity. This masking effect could not be attributed to the local directional changes, symmetry, or perceptual closure of the inducers near the target. These results provide strong evidence for a high-level locus of interference in object substitution masking. (Contains 4 footnotes and 6 figures.)