A result of Fiz Pontiveros shows that if $A$ is a random subset of $ZN$ where each element is chosen independently with probability $N-1/2+o(1)$, then with high probability every Freiman homomorphism defined on $A$ can be extended to a Freiman homomorphism on the whole of $ZN$. In this paper we improve the bound to $CN-2/3(\log N)1/3$, which is best possible up to the constant factor.