diff --git a/CHANGELOG.md b/CHANGELOG.md
index 32ca233db..befbff426 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 5.5.2 / 4.5.2
+
+* Fixed bug in `toJS` not handling `null` values correctly. Fixes [#1557](https://github.com/mobxjs/mobx/issues/1557) through [#1783](https://github.com/mobxjs/mobx/pull/1783) by [@wangyiz4262](https://github.com/wangyiz4262)
+
 # 5.5.1 / 4.5.1
 
 * `toJS` now has a `recurseEverything` everything option, that even detects and converts observable objects that are "behind" non-observable objects. See [#1699](https://github.com/mobxjs/mobx/pull/1699) by [wangyiz4262](https://github.com/wangyiz4262)
diff --git a/package.json b/package.json
index 4a42cc236..b2d28283a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "mobx",
-  "version": "5.5.1",
+  "version": "5.5.2",
   "description": "Simple, scalable state management.",
   "main": "lib/mobx.js",
   "umd:main": "lib/mobx.umd.js",