  We present high-resolution, time-resolved optical spectroscopy of the black
hole X-ray transient Swift J1753.5-0127. Our optical spectra do not show
features that we can associate with the companion star. However we do observe
broad, double-peaked emission lines, typical of an accretion disc. We show that
the mass of the compact object is likely $>7.4\pm1.2M_{\odot}$, much higher
than previous suggestions of a low-mass ($<5M_{\odot}$) black hole.
