Runtime enforcement (RE) is a technique to ensure that the (un-trustworthy) output of a black-box system satisfies some desired properties. In RE, the output of the running system, modeled as a stream of events, is fed into an enforcement monitor. The monitor ensures that the stream complies with a certain property, by delaying or modifying events if necessary. This paper deals with predictive runtime enforcement, where the system is not entirely black-box, but we know something about its behavior. This a-priori knowledge about the system allows to output some events immediately , instead of delaying them until more events are observed, or even blocking them permanently. This in turn results in better enforcement policies. We also show that if we have no knowledge about the system, then the proposed enforcement mechanism reduces to a classical non-predictive RE framework. All our results are formalized and proved in the Isabelle theorem prover.