Muon Knight-shift measurement are experimentally rather challenging as in most setups one does not have a direct way of measuring the external magnetic field applied to the sample. Here we show, a way to overcome this problem and suggest a suitable sample mounting and correcting scheme. This enables us to quantitatively determine the correct Knight-shift values even in extreme sample environments where a separate measurement of the externally applied magnetic field by means of NMR or additional µSR is not feasible or practical.