Module systems are important for software engineering: they facilitate code reuse without compromising the correctness of programs. However, they still lack some flexibility: first, they do not allow mutually recursive definitions to span module boundaries ; second, definitions inside modules are bound early, and cannot be overridden later, as opposed to inheritance and overriding in class-based object-oriented languages, which follow the late binding semantics. This paper examines an alternative, hybrid idea of modularization concept, called mixin modules. We develop a language of call-by-value mixin modules with a reduction semantics, and a sound type system for it, guaranteeing that programs will run correctly.