Mean out-of-transit Lyman-α spectrum of GJ 436 measured with HST-COS observations from program GO-15174 (red spectrum with blue uncertainty bars). For comparison, we plot the mean out-of-transit spectrum measured with HST-STIS in black. The spectra are centered in the stellar rest frame. The intrinsic Lyman-α emission line of GJ 436 likely possesses a single-peaked Voigt shape (Bourrier et al. 2015), but the core of the line is absorbed bythe ISM, producing a double-peaked feature when observed from the Earth.