diff --git a/CHANGELOG.md b/CHANGELOG.md
index e862aee..104c05a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.1.20
+
+* Close worker `outputStream` on `cancel`.
+
 ## 0.1.19
 
 * Work around https://github.com/dart-lang/sdk/issues/35874.
diff --git a/lib/src/driver/driver_connection.dart b/lib/src/driver/driver_connection.dart
index 6dd9826..f30bf84 100644
--- a/lib/src/driver/driver_connection.dart
+++ b/lib/src/driver/driver_connection.dart
@@ -77,7 +77,10 @@ class StdDriverConnection implements DriverConnection {
   }
 
   @override
-  Future cancel() => _messageGrouper.cancel();
+  Future cancel() async {
+    await _outputStream.close();
+    await _messageGrouper.cancel();
+  }
 }
 
 /// [DriverConnection] that works with an isolate via a [SendPort].
diff --git a/pubspec.yaml b/pubspec.yaml
index 58d70cd..b2e3641 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: bazel_worker
-version: 0.1.19
+version: 0.1.20
 
 description: Tools for creating a bazel persistent worker.
 author: Dart Team <misc@dartlang.org>