Emotional expressivity is essential for successful Human-Robot Interaction. However, robots often have different levels of expressivity in their face and voice. Here we ask whether this modality mismatch influences human behaviour and perception of the robot. Participants played a cooperative task with a robot that displayed matched and mismatched smiling expressions in the face and voice. Emotional expressivity did not influence acceptance of robot's recommendations or subjective evaluations of the robot. However, we found that the robot had overall a higher social influence than a virtual character, and was evaluated more positively.