Region around the DLA in the spectrum of Q 1218+0832 shown together with the filter transmission curve (dotted line) of the 63 Å-wide narrow-band filter NB391_7 used in this study (see also Fig. 2 in Geier et al. 2019). The vertical dotted line shows the expected position of Lyman-α at the redshift of z = 2.2261 measured from low-ionisation metal lines in Geier et al. (2019). The filter, although designed for other purposes, matches the DLA trough perfectly.