Virtual Machines (VM) tend to evolve over their life cycle with features being added regularly and a growing footprint. In a VM designed for resource constrained environments this trend deteriorates the VM’s primary quality. We present how extensibility is implemented in the Ribbit Scheme VM that is both compact and portable to multiple languages. Our approach adds annotations to the VM’s source code allowing the compiler to generate the source code of a specialized VM extended with user-defined primitives and with needless ones removed. This give the best of both worlds: an extensible VM packed with all and only the features needed by the source code, while maintaining a small code footprint.