diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 3593785043..996164b93e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -206,6 +206,14 @@ rustup toolchain link stage2 build/x86_64-unknown-linux-gnu/stage2
 rustup override set stage2
 ```
 
+Important: You need to delete the Miri cache when you change the stdlib; otherwise the
+old, chached version will be used. On Linux, the cache is located at `~/.cache/miri`; the exact
+location is printed after the library build: "A libstd for Miri is now available in ...".
+
+Note: `./x.py --stage 2 compiler/rustc` currently errors with `thread 'main'
+panicked at 'fs::read(stamp) failed with No such file or directory (os error 2)`,
+you can simply ignore that error; Miri will build anyway.
+
 For more information about building and configuring a local compiler,
 see <https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html>.