We analyzed helium and neon in 24 samples from between 3,607 and 3,767 m (i.e., down to 2 m above the lake-ice interface) of the accreted ice frozen to the ceiling of Lake Vostok. Within uncertainties, the neon budget of the lake is balanced, the neon supplied to the lake by the melting of glacier ice being compensated by the neon exported by lake ice. The helium concentration in the lake is about 12 times more than in the glacier ice, with a measured ³He/⁴He ratio of 0.12 ± 0.01 R_a. This shows that Lake Vostok's waters are enriched by a terrigenic helium source. The ³He/⁴He isotope ratio of this helium source was determined. Its radiogenic value (0.057 × R_a) is typical of an old continental province, ruling out any magmatic activity associated with the tectonic structure of the lake. It corresponds to a low geothermal heat flow estimated at 51 mW/m².