We reached out to the Foundation around April to discuss this problem and the consensus with the legal council at that time seemed to be: The original port of apfloat code should be licensed under UIUC as it is most likely a derived work from the LLVM code. The COPYRIGHT.md file probably needs to note this fact. Subsequent changes to the code were almost certainly done under an Apache2/MIT dual license as that is what the rust-lang/rust repo states. We later learned that the GH TOS mandates that contributions are made under the same licensing terms as the repo unless specifically noted otherwise. "In its current state, the apfloat port is therefore likely a combination of code from the original port licensed under UIUC License, and code from subsequent contributions licensed under Apache/MIT." "The easiest / least laborious route is just to update the COPYRIGHT file to include a notice that the initial port of apfloat in src/librustc_apfloat is licensed under the UIUC License, and subsequent modifications are licensed Apache/MIT. While the latter conclusion (re: subsequent contributions) is not 100% certain, this approach at least brings the codebase into compliance with the UIUC License and honors the intentions of all contributors the best we can under the circumstances."