diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 0cf9d34c..581dd349 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,5 +1,5 @@
 {
-  "packages/stream": "4.2.0",
+  "packages/stream": "4.2.1",
   "packages/stream-assert": "1.2.0",
   "packages/stream-common": "2.1.1",
   "packages/stream-jest": "2.2.0",
diff --git a/package-lock.json b/package-lock.json
index 74d55709..18ad62cb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10001,7 +10001,7 @@
     },
     "packages/stream": {
       "name": "@johngw/stream",
-      "version": "4.2.0",
+      "version": "4.2.1",
       "dependencies": {
         "@johngw/stream-common": "^2.1.1",
         "@types/node": "^25.0.0",
diff --git a/packages/stream/CHANGELOG.md b/packages/stream/CHANGELOG.md
index 415b9bf8..5fb6fbbe 100644
--- a/packages/stream/CHANGELOG.md
+++ b/packages/stream/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## [4.2.1](https://github.com/jg-wright/stream/compare/stream-v4.2.0...stream-v4.2.1) (2026-06-08)
+
+
+### Bug Fixes
+
+* ensure underlyingSource defaults to an empty object in _addController ([c3f38ad](https://github.com/jg-wright/stream/commit/c3f38ad496f53796e4f93b164f3ef3cecf8b2a85))
+
 ## [4.2.0](https://github.com/jg-wright/stream/compare/stream-v4.1.0...stream-v4.2.0) (2026-06-08)
 
 
diff --git a/packages/stream/package.json b/packages/stream/package.json
index 2096b5ee..b11aac2a 100644
--- a/packages/stream/package.json
+++ b/packages/stream/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@johngw/stream",
-  "version": "4.2.0",
+  "version": "4.2.1",
   "type": "module",
   "description": "Reactive programming tools using the WHATWG Streams API.",
   "keywords": [