diff --git a/portable-atomic-util/CHANGELOG.md b/portable-atomic-util/CHANGELOG.md
index c835f2fb..bc8f557e 100644
--- a/portable-atomic-util/CHANGELOG.md
+++ b/portable-atomic-util/CHANGELOG.md
@@ -12,7 +12,9 @@ Note: In this file, do not use the hard wrap in the middle of a sentence for com
 
 ## [Unreleased]
 
-- Add `portable_atomic_unstable_coerce_unsized` cfg option (requires Rust nightly)
+- Add unstable `portable_atomic_unstable_coerce_unsized` cfg (requires Rust nightly). ([#195](https://github.com/taiki-e/portable-atomic/pull/195), thanks @brodycj)
+
+- Respect [`RUSTC_BOOTSTRAP=-1` recently added in nightly](https://github.com/rust-lang/rust/pull/132993) in rustc version detection. ([5b2847a](https://github.com/taiki-e/portable-atomic/commit/5b2847a8b99aa2a57a6c80f5a47327b2764f08cc))
 
 ## [0.2.3] - 2024-10-17
 
diff --git a/portable-atomic-util/README.md b/portable-atomic-util/README.md
index 47607c89..cf9c6928 100644
--- a/portable-atomic-util/README.md
+++ b/portable-atomic-util/README.md
@@ -54,13 +54,16 @@ Or set environment variable:
 RUSTFLAGS="--cfg portable_atomic_unstable_coerce_unsized" cargo ...
 ```
 
-- <a name="portable-atomic-unstable-coerce-unsized"></a>**`--cfg portable_atomic_unstable_coerce_unsized`**<br> support standard coercing of `Arc<T>` to `Arc<U>`
+- <a name="optional-cfg-unstable-coerce-unsized"></a>**`--cfg portable_atomic_unstable_coerce_unsized`**<br>
+  Support coercing of `Arc<T>` to `Arc<U>` as in `std::sync::Arc`.
 
-<!-- TODO: add standard coercing of `Weak<T>` to `Weak<U>` as well, with testing & documentation updates -->
+  <!-- TODO: add coercing of `Weak<T>` to `Weak<U>` as well, with testing & documentation updates -->
 
-This coercing requires Rust nightly to compile (with help from [unstable `CoerceUnsized` trait](https://doc.rust-lang.org/nightly/core/ops/trait.CoerceUnsized.html)).
+  This coercing requires Rust nightly to compile (with help from [unstable `CoerceUnsized` trait](https://doc.rust-lang.org/nightly/core/ops/trait.CoerceUnsized.html)).
 
-See [this issue comment](https://github.com/taiki-e/portable-atomic/issues/143#issuecomment-1866488569) for another known workaround.
+  See [this issue comment](https://github.com/taiki-e/portable-atomic/issues/143#issuecomment-1866488569) for another known workaround.
+
+  **Note:** This cfg is unstable and outside of the normal semver guarantees and minor or patch versions of portable-atomic-util may make breaking changes to them at any time.
 
 <!-- tidy:crate-doc:end -->
 
diff --git a/portable-atomic-util/src/lib.rs b/portable-atomic-util/src/lib.rs
index a59a9c3a..67f5b26a 100644
--- a/portable-atomic-util/src/lib.rs
+++ b/portable-atomic-util/src/lib.rs
@@ -48,13 +48,16 @@ Or set environment variable:
 RUSTFLAGS="--cfg portable_atomic_unstable_coerce_unsized" cargo ...
 ```
 
-- <a name="portable-atomic-unstable-coerce-unsized"></a>**`--cfg portable_atomic_unstable_coerce_unsized`**<br> support standard coercing of `Arc<T>` to `Arc<U>`
+- <a name="optional-cfg-unstable-coerce-unsized"></a>**`--cfg portable_atomic_unstable_coerce_unsized`**<br>
+  Support coercing of `Arc<T>` to `Arc<U>` as in `std::sync::Arc`.
 
-<!-- TODO: add standard coercing of `Weak<T>` to `Weak<U>` as well, with testing & documentation updates -->
+  <!-- TODO: add coercing of `Weak<T>` to `Weak<U>` as well, with testing & documentation updates -->
 
-This coercing requires Rust nightly to compile (with help from [unstable `CoerceUnsized` trait](https://doc.rust-lang.org/nightly/core/ops/trait.CoerceUnsized.html)).
+  This coercing requires Rust nightly to compile (with help from [unstable `CoerceUnsized` trait](https://doc.rust-lang.org/nightly/core/ops/trait.CoerceUnsized.html)).
 
-See [this issue comment](https://github.com/taiki-e/portable-atomic/issues/143#issuecomment-1866488569) for another known workaround.
+  See [this issue comment](https://github.com/taiki-e/portable-atomic/issues/143#issuecomment-1866488569) for another known workaround.
+
+  **Note:** This cfg is unstable and outside of the normal semver guarantees and minor or patch versions of portable-atomic-util may make breaking changes to them at any time.
 
 <!-- tidy:crate-doc:end -->
 */