diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9aff4b8a..bfda4d99 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ Features
 
 - Added a new library `(cycone concurrent)` with support for atomics, immutability, and shared objects.
 - Relocated existing libraries to `(cyclone match)` and `(cyclone test)`.
+- Extended `mutex-lock!` to support an optional `timeout` parameter, per the SRFI 18 spec.
 
 Bug Fixes