Sturm–Schrödinger equations $H\psi = EW\psi$ with $H \neq H^{\dagger}$ and $W \neq W^{\dagger} \neq I$ are considered, with a weak point of the theory lying in the purely numerical matrix- inversion form of the double-series definition of the necessary metric operator 𝛩 in the physical Hilbert space of states [M Znojil, J. Phys. A: Math. Theor. 41, 215304 (2008)]. This shortcoming is removed here via an amended, single-series definition of 𝛩.