diff --git a/src/error-handling/converting-error-types-example.md b/src/error-handling/converting-error-types-example.md
index 9cbd6874..1e83b470 100644
--- a/src/error-handling/converting-error-types-example.md
+++ b/src/error-handling/converting-error-types-example.md
@@ -52,8 +52,9 @@ Key points:
 * The `username` variable can be either `Ok(string)` or `Err(error)`.
 * Use the `fs::write` call to test out the different scenarios: no file, empty file, file with username.
 
-It is good practice for all error types to implement `std::error::Error`, which requires `Debug` and
-`Display`. It's generally helpful for them to implement `Clone` and `Eq` too where possible, to make
+It is good practice for all error types that don't need to be `no_std` to implement `std::error::Error`, which requires `Debug` and `Display`. The `Error` crate for `core` is only available in [nightly](https://github.com/rust-lang/rust/issues/103765), so not fully `no_std` compatible yet.
+
+It's generally helpful for them to implement `Clone` and `Eq` too where possible, to make
 life easier for tests and consumers of your library. In this case we can't easily do so, because
 `io::Error` doesn't implement them.