Detector blinding attacks have been proposed in the last few years, and they could potentially threaten the security of quantum key distribution systems. Even though such attacks are technically challenging to implement, it is important to consider countermeasures to avoid information leakage. In this paper, we present a countermeasure against these kinds of attacks based on the use of multipixel detectors. We show that with this method, we are able to estimate an upper bound on the information an eavesdropper could have on the key exchanged. Finally, we test a multipixel detector based on superconducting nanowire single-photon detectors to show it can fulfill all the requirements for our countermeasure to be effective.