Summary: We substantially refine the theory of singular principal bundles introduced in [A. Schmitt, Int. Math. Res. Not. 2002, No.23, 1183–1209 (2002; Zbl 1034.14017)]. In particular, we show that we need only honest singular principal bundles in our compactification. These are objects which carry the structure of a rational principal bundle in the sense of Ramanathan. Moreover, we arrive at a much simpler semistability condition. In the case of a semisimple group, this is just the Gieseker version of Ramanathan’s semistability condition for the corresponding rational principal \(G\)-bundle.