diff --git a/src/licenses.md b/src/licenses.md
index 06cd8ae6b..aa8286714 100644
--- a/src/licenses.md
+++ b/src/licenses.md
@@ -3,3 +3,45 @@
 The `rustc` compiler source and standard library are dual licensed under the [Apache License v2.0](https://github.com/rust-lang/rust/blob/master/LICENSE-APACHE) and the [MIT License](https://github.com/rust-lang/rust/blob/master/LICENSE-MIT) unless otherwise specified.
 
 Detailed licensing information is available in the [COPYRIGHT document](https://github.com/rust-lang/rust/blob/master/COPYRIGHT) of the `rust-lang/rust` repository.
+
+## Guidelines for reviewers
+
+In general, reviewers need to be looking not only for the code quality of contributions but also
+that they are properly licensed.
+We have some tips below for things to look out for when reviewing, but if you ever feel uncertain
+as to whether some code might be properly licensed, err on the safe side — reach out to the Council
+or Compiler Team Leads for feedback!
+
+Things to watch out for:
+
+- The PR author states that they copied, ported, or adapted the code from some other source.
+- There is a comment in the code pointing to a webpage or describing where the algorithm was taken
+from.
+- The algorithm or code pattern seems like it was likely copied from somewhere else.
+- When adding new dependencies, double check the dependency's license.
+
+In all of these cases, we will want to check that source to make sure it it is licensed in a way
+that is compatible with Rust’s license.
+
+Examples
+
+- Porting C code from a GPL project, like GNU binutils, is not allowed. That would require Rust
+itself to be licensed under the GPL.
+- Copying code from an algorithms text book may be allowed, but some algorithms are patented.
+
+## Porting
+
+Contributions to rustc, especially around platform and compiler intrinsics, often include porting
+over work from other projects, mainly LLVM and GCC.
+
+Some general rules apply:
+
+- Copying work needs to adhere to the original license
+    - This applies to direct copy & paste
+    - This also applies to code you looked at and ported
+
+In general, taking inspiration from other codebases is fine, but please exercise caution when
+porting code.
+
+Ports of full libraries (e.g. C libraries shipped with LLVM) must keep the license of the original
+library.