Voice has been suggested to be a cue of cooperativeness since several acoustic features influence cooperativeness ratings. However, no experimental study has investigated whether these acoustic features are associated with actual and not only perceived cooperativeness. Still, this question is crucial to disentangle whether inferences of traits from voices only reveal stereotypes or enable hearers to extract useful information with respect to cooperativeness. To fill this gap, we quantified cooperativeness of 64 native French men through a one-shot public good game, and measured mean fundamental frequency, pitch variations, roughness and breathiness from spontaneous speech. We found that men with lower-pitched voices and with greater pitch variations were more cooperative. This is the first evidence of acoustic correlates of cooperativeness. Combined with the literature on face-based cooperation detection, we suggest that more than one sensory modality advertise cooperativeness and could therefore be simultaneously used to assess cooperativeness more accurately.