The lattice strain induced both by substitutional and clustered B in B-implanted Ge samples has been investigated by means of high resolution x-ray diffraction (HRXRD). The main results can be summarized as follows: while substitutional (i.e., electrically active) B exhibits a negative strain, clustered (i.e., electrically inactive) B reverses the lattice strain from negative to positive values, the latter being much higher with respect to those found for clustered B in Si. In particular, the lattice volume modification for each B atom (ΔV) induced by substitutional (ΔVSub) and clustered (ΔVCl) B is ΔVSub=−12.4 Å3 and ΔVCl=+14.8 Å3, respectively. These unexpected results demonstrate the ability of HRXRD to quantitatively detect the amount of electrically inactive (and active) B.