Just-in-Time compilation consists in interleaving program interpretation and compilation at run-time, to achieve better performance than standard interpretation. While some of the execution time is spent compiling, a JIT compiler can leverage run-time information to make speculative optimizations. These optimizations create optimized versions of functions given some assumptions. While static compilers have been the topic of many formal verification works, few have tackled JIT compilation verification. We present our ongoing work about formal verification of a Just-in-Time compiler.