Current models of the evolution of the known extrasolar planetary systems need to incorporate orbital migration and/or gravitational interactions among giant planets to explain the presence of large bodies close to their parent stars. These processes could also lead to planets being ingested by their parent stars, which would alter the relative abundances of elements heavier than helium in the stellar atmospheres. In particular, the abundance of the rare 6Li isotope, which is normally destroyed in the early evolution of solar-type stars but preserved intact in the atmospheres of giant planets, would be boosted substantially. 6Li has not hitherto been observed reliably in a metal-rich star, where metallicity refers to the total abundance of elements heavier than helium. Here we report the discovery of 6Li in the atmosphere of the metal-rich solar-type star HD82943, which is known to have an orbiting giant planet. The presence of 6Li can probably be interpreted as evidence for a planet (or planets) having been engulfed by the parent star.