The present invention relates to dimers comprising a first polypeptide and a second polypeptide, wherein each of said first and second polypeptide comprises at least one immunoglobulin single variable domain (ISVD) and a C-terminal extension comprising a cysteine moiety (preferably at the C-terminus), wherein said first polypeptide and said second polypeptide are covalently linked via a disulfide bond between the cysteine moiety of said first polypeptide and the cysteine moiety of said second polypeptide, in which the dimer outperformed the benchmark constructs, e.g. cognate multivalent and multispecific constructs, in various assays. The present invention provides methods for making the dimers of the invention.