A circuit internal to a programmable integrated circuit for preventing laser interrogation of the programmable integrated circuit includes a sense resistor connected between a deep n-well and a source of bias voltage for the deep n-well. A voltage-sensing circuit is coupled across the sense resistor to measure voltage across the sense resistor. A tamper trigger circuit responsive to the voltage sensing circuit generates a tamper signal in response to a voltage sensed in the voltage sensing circuit having a magnitude greater than a threshold value.