The optical sensor package comprises an optical sensor device with a sensor element arranged inside a housing comprising a cap. A diffuser is arranged in an aperture of the cap opposite the sensor element and prolongs the cap in the aperture or closes the aperture. The method comprises forming a cap with an aperture, arranging a diffusing material in the aperture, thus forming a diffuser, and after forming the diffuser, arranging an optical sensor device with a sensor element inside a housing that includes the cap, such that the sensor element is opposite the diffuser.