  We present a detailed time-resolved photometric study of the ultra-compact
X-ray binary candidate 4U 1812-12. The multicolor light curves obtained with
HiPERCAM on the 10.4-m Gran Telescopio Canarias show an aprox 114 min
modulation similar to a superhump. Under this interpretation, this period
should lie very close to the orbital period of the system. Contrary to what its
other observational properties suggest (namely, persistent dim luminosity, low
optical-to-X-ray flux ratio and lack of hydrogen features in the optical
spectrum), this implies that 4U1812-12 is most likely not an ultra-compact
X-ray binary, which are usually defined as systems with orbital periods lower
than 80 min. We discuss the nature of the system, showing that a scenario in
which 4U 1812-12 is the progenitor of an ultra-compact X-ray binary may
reconcile all the observables.
