Stack of DR9 BOSS spectra where a damped Lyman-α system is seen at an absorpstion redshift higher than 3.385 with a column density N(H i) ≥ 10^20.5 cm^-2. The spectra are normalized to unity near 1280 Å in the quasar rest frame. Owing to the presence of the DLA, the flux is expected to be zero at observed wavelengths below  ~4100 Å (e.g. below the Lyman limit of all DLAs). This is not the case in the very blue part of the spectrum (λ_obs ≤ 4000 Å) where the mean observed flux appears to increase (spuriously).