Summary: eSTREAM ciphers, Trivium in particular, have shown to be vulnerable against fault attacks. Differential fault analysis and a number of its variants pose a major threat against Trivium which exploits the weakness in nonlinearity and reversibility of Trivium function. This work analyses the fault attack on Trivium and shows how Cellular Automata (CA) can effectively be deployed to prevent these attacks. CASTREAM and CAR30 are two popular CA based stream ciphers which exploit the fast evolution of CA providing high nonlinearity. This paper performs the security analysis of CASTREAM and CAR30 and they are shown to be resistant against fault attacks.