diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0ac09c4..8fc837b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,8 @@
 # Changelog
+
+## Unreleased
+- Add schema validation: Input Objects must not contain non-nullable circular references (#492)
+
 ## v0.13.0
 This release brings several breaking changes. Please refer to [UPGRADE](UPGRADE.md) document for details.
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 399716c..d51a0ac 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -10,8 +10,9 @@ For smaller contributions just use this workflow:
 * Fork the project.
 * Add your features and or bug fixes.
 * Add tests. Tests are important for us.
-* Check your changes using `composer check-all`
-* Send a pull request
+* Check your changes using `composer check-all`.
+* Add an entry to the [Changelog's Unreleases section](CHANGELOG.md#unreleased).
+* Send a pull request.
 
 ## Setup the Development Environment
 First, copy the URL of your fork and `git clone` it to your local machine.