In this paper, we present an effective approach to compensate for the substrate-induced bianisotropy in optical metamaterials, thus making them bianisotropy-free to outside observers. This magnetoelectric coupling compensation for the system is achieved by adding an ultrathin superstrate, with a judicious choice of its thickness and permittivity values, directly on top of the metamaterial. A specific example will be illustrated using the well-known multilayer fishnet nanostructure. Both the extracted nonlocal effective medium parameters and the induced electric/magnetic dipole moments calculated from volumetric microscopic fields will be presented to validate the proposed methodology. This study will be beneficial to the design of future optical metamaterials, especially their related fabrication and characterization.