LEX is a stream cipher based on the round transformation of the AES block cipher, and it was selected for the final phase evaluation of the eSTREAM project. LEX is 2.5 times faster than AES both in software and in hardware. In this paper, we present a differential fault attack on LEX. The fault model assumes that the attacker is able to flip a random bit of the internal state of the cipher but cannot control the exact location of the induced fault. Our attack requires 40 faults, and recovers the secret key with 216 operations.