diff --git a/CHANGELOG.md b/CHANGELOG.md
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@@ -1,5 +1,10 @@
 # Changelog
 
+## 3.1.1 (Unreleased)
+
+### Improvements
+ * `Address.isContract`: switched from `extcodehash` to `extcodesize` for less gas usage. ([#2311](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2311))
+
 ## 3.1.0 (2020-06-23)
 
 ### New features