Interoperability across software languages is an important practical topic — especially in the context of software migration, where foreign function interfaces can help to replace legacy code fragments with calls to existing alternatives. In this paper, we take a deep dive into investigating and tackling the challenges involved with achieving interoperability between C and BabyCobol. The latter is a little domain-specific language, condensing challenges found in compiling legacy languages — borrowing directly from COBOL’s data philosophy — into one quickly implementable language. In this paper, we introduce Crossover, a compiler designed specifically to showcase the interoperability and the details of connecting a COBOL-like language with PICTURE clauses and re-entrant procedures, to C with primitive types and struct composites. Crossover features a C library for bridging the gap in overcoming the differences between the data representations native to the respective languages. We illustrate the design process of Crossover and demonstrate its usage to provide a strategy to achieve interoperability between legacy and modern languages. From a practical perspective, this directly enables C programmers to contribute to the maintenance of (as well as migration away from) legacy systems. The described process is aimed to be a blueprint for how interoperability can be achieved between full-fledged COBOL and modern (C-like) programming languages, enabling developers versed in either language to contribute to the maintenance of legacy systems.