Pallene is a statically typed subset of the Lua programming language, designed to act as a system-language counterpart to Lua’s scripting, and used to write lower-level libraries and extension modules for Lua. In this sense, Pallene is a companion language, always intended to be used side-by-side with Lua, sharing its runtime. Pallene, both as a system-language counterpart to Lua and as a bridge between Lua and foreign languages, must provide a mechanism to interact with libraries and system services written in a low-level language like C. To this end, we present a Foreign Function Interface (FFI) design and implementation for Pallene, which allows for calling external functions that follow C calling conventions and manipulating C data representations directly. Our design balances flexibility and safety following an empirical approach, wherein we prefer to sacrifice hypothetical flexibility unless we see a real use case that forces us to compromise on safety. Our implementation aims to be as portable as Pallene, as well as performant and simple. Since Pallene s implementation already depends on a C compiler, the FFI aggressively uses the already available C compiler to its advantage. This way, we can directly use foreign libraries header files, enabling the FFI to verify the correctness of function bindings and to use macro definitions.