In a portable electronic device, a temperature sensor (1) is provided for sensing an ambient temperature (T R ) of the portable electronic device. At least one other temperature sensor (3) is provided for sensing a temperature (T I ) inside the portable electronic device. The portable electronic device further comprises a set of components (2) radiating heat in an active state in response to the consumption of electrical energy. A calibration module (5) is adapted to conduct a calibration measurement during or in connection with an active state of at least a first component out of the set, and is adapted to determine a set of calibration parameters (c1) in response to the calibration measurement for adjusting the at least one sensed inside temperature (T 1 ). A compensator (4) is provided for determining a compensated ambient temperature (T A ) dependent on at least the sensed ambient temperature (T S ) and the at least one adjusted sensed inside temperature (c1, T 1 ).