An environmental seal is formed around a square sensor disposed beneath a circular button cap within a button assembly. The button assembly includes shelf portions each extending separately into the interior of the assembly from a sidewall of the assembly. Portions of the sidewall are exposed between the shelf portions large enough to permit the four corners of the square sensor to contact the sidewall. The button cap is set above the sensor, resting upon the shelf portions. A first sealant bonds the top faces of the shelf portions to the bottom of the button cap. A second sealant bonds the edges of the sidewall to the corners of the sensor. The second sealant interfaces with the first sealant to form a complete environmental seal.