A method for use in earth-fault protection in a three-phase electric network, comprising: detecting a phase-to-earth fault in the three-phase electric network ; determining at a measuring point in the three-phase electric network , for each of the three phases (A, B, C) of the three-phase electric network, a change in the phase current due to the detected phase-to-earth fault, the determining comprising determining, for each of the three phases (A, B, C) of the three-phase electric network, a difference between a fundamental frequency component of the phase current during the phase-to-earth fault and the fundamental frequency component of the phase current before the phase-to-earth fault, and/or determining, for each of the three phases (A, B, C) of the three-phase electric network , and for at least one harmonic frequency, which is an integer multiple of the fundamental frequency of the phase current, a difference between a harmonic frequency component of the phase current during the phase-to-earth fault and the harmonic frequency component of the phase current before the phase-to-earth fault; determining an estimate of an earth-fault current in a point of the detected phase-to-earth fault passing through the measuring point on the basis of the determined changes in the phase currents of the three phases of the three-phase electric network by using at least one of: an equation based on a change in a negative-sequence current component, an equation based on a change in a positive-sequence current component, an equation based on changes of the phase currents; determining , if the estimate of the earth-fault current represents an actual earth-fault current or an apparent earth-fault current; and in response to determining that the estimate of the earth-fault current represents the actual earth-fault current, determining that the estimate of the earth-fault current is valid. detecting a phase-to-earth fault in the three-phase electric network ; determining at a measuring point in the three-phase electric network , for each of the three phases (A, B, C) of the three-phase electric network, a change in the phase current due to the detected phase-to-earth fault, the determining comprising determining, for each of the three phases (A, B, C) of the three-phase electric network, a difference between a fundamental frequency component of the phase current during the phase-to-earth fault and the fundamental frequency component of the phase current before the phase-to-earth fault, and/or determining, for each of the three phases (A, B, C) of the three-phase electric network , and for at least one harmonic frequency, which is an integer multiple of the fundamental frequency of the phase current, a difference between a harmonic frequency component of the phase current during the phase-to-earth fault and the harmonic frequency component of the phase current before the phase-to-earth fault; determining an estimate of an earth-fault current in a point of the detected phase-to-earth fault passing through the measuring point on the basis of the determined changes in the phase currents of the three phases of the three-phase electric network by using at least one of: an equation based on a change in a negative-sequence current component, an equation based on a change in a positive-sequence current component, an equation based on changes of the phase currents; determining , if the estimate of the earth-fault current represents an actual earth-fault current or an apparent earth-fault current; and in response to determining that the estimate of the earth-fault current represents the actual earth-fault current, determining that the estimate of the earth-fault current is valid. <EOS>