Magellan/MagE spectrum (black) of the host galaxy of eRO-QPE1. Overlaid in orange is the best-fit template that was used to measure the host velocity dispersion. The inset shows the region around the Mg I b triplet to illustrate the quality of the fit. Grey bands indicate host galaxy emission lines, which were excluded from the fit. The spectrum was convolved with a Gaussian kernel with a width of 5 pixels for clarity.