Near-infrared surveys have revealed a substantial population of faint galaxies that are extremely red in their optical to near-infrared colours(1). These enigmatic galaxies are about as numerous as faint quasars(1). The extremely red colours could arise either because of an absence of recently formed stars, implying that the galaxies formed almost all of their stars at very high redshifts(2), or because the galaxies contain large amounts of dust, which reddens the light by preferentially absorbing the shorter-wavelength radiation. Determining why these objects are red will help us to understand the early evolution of galaxies. The object HR10, at a redshift of z = 1.44 (refs 1, 3), is considered the archetype of the extremely red galaxies. Here we report the detection of continuum emission from warm dust in HR10, demonstrating that it is a dusty galaxy undergoing a burst of massive-star formation. Our result provides a clear example of a high-redshift galaxy where the star-formation rate inferred from the ultraviolet luminosity (the usual method at these redshifts) would be underestimated by a factor of more than 500, showing that great caution must be used to infer the global star-formation history of the Universe from optical and ultraviolet observations(4).