diff --git a/CHANGELOG.md b/CHANGELOG.md
index d43d717..0041245 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 2.5.1-dev
+
+* Fix an unhandled async error when completing a `CancelableCompleter` with a
+  `Future.error` after it was already canceled.
+
 ## 2.5.0
 
 * Stable release for null safety.
diff --git a/lib/src/cancelable_operation.dart b/lib/src/cancelable_operation.dart
index c321078..b1cac55 100644
--- a/lib/src/cancelable_operation.dart
+++ b/lib/src/cancelable_operation.dart
@@ -189,7 +189,7 @@
     final future = value as Future<T>;
     if (_isCanceled) {
       // Make sure errors from [value] aren't top-leveled.
-      future.catchError((_) {});
+      future..then<void>((_) {}).onError((_, __) {});
       return;
     }
 
diff --git a/lib/src/future_group.dart b/lib/src/future_group.dart
index 3a6291f..2968b0b 100644
--- a/lib/src/future_group.dart
+++ b/lib/src/future_group.dart
@@ -77,7 +77,7 @@
       if (!_closed) return null;
       if (onIdleController != null) onIdleController.close();
       _completer.complete(_values.whereType<T>().toList());
-    }).catchError((Object error, StackTrace stackTrace) {
+    }).onError<Object>((error, stackTrace) {
       if (_completer.isCompleted) return null;
       _completer.completeError(error, stackTrace);
     });
diff --git a/lib/src/null_stream_sink.dart b/lib/src/null_stream_sink.dart
index 34b100b..b61b2bc 100644
--- a/lib/src/null_stream_sink.dart
+++ b/lib/src/null_stream_sink.dart
@@ -53,7 +53,7 @@
           // Don't top-level the error. This gives the user a change to call
           // [close] or [done], and matches the behavior of a remote endpoint
           // experiencing an error.
-          ..catchError((_) {});
+          ..onError((_, __) {});
 
   @override
   void add(T data) {
diff --git a/lib/src/stream_sink_completer.dart b/lib/src/stream_sink_completer.dart
index 10e549d..c5a098c 100644
--- a/lib/src/stream_sink_completer.dart
+++ b/lib/src/stream_sink_completer.dart
@@ -166,7 +166,7 @@
       sink
           .addStream(_controller!.stream)
           .whenComplete(sink.close)
-          .catchError((_) {});
+          .onError((_, __) {});
     }
 
     // If the user has already asked when the sink is done, connect the sink's
diff --git a/lib/src/stream_sink_transformer/handler_transformer.dart b/lib/src/stream_sink_transformer/handler_transformer.dart
index d6f188e..5f9e0b4 100644
--- a/lib/src/stream_sink_transformer/handler_transformer.dart
+++ b/lib/src/stream_sink_transformer/handler_transformer.dart
@@ -101,7 +101,7 @@
   _SafeCloseSink(StreamSink<T> inner) : super(inner);
 
   @override
-  Future close() => super.close().catchError((_) {});
+  Future close() => super.close().onError((_, __) {});
 }
 
 /// A function to pass as a [StreamTransformer]'s `handleDone` callback.
diff --git a/lib/src/stream_sink_transformer/stream_transformer_wrapper.dart b/lib/src/stream_sink_transformer/stream_transformer_wrapper.dart
index 2afcbff..373a650 100644
--- a/lib/src/stream_sink_transformer/stream_transformer_wrapper.dart
+++ b/lib/src/stream_sink_transformer/stream_transformer_wrapper.dart
@@ -40,7 +40,7 @@
       // Ignore any errors that come from this call to [_inner.close]. The
       // user can access them through [done] or the value returned from
       // [this.close], and we don't want them to get top-leveled.
-      _inner.close().catchError((_) {});
+      _inner.close().onError((_, __) {});
     });
   }
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 3c8dd95..47c653f 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: async
-version: 2.5.0
+version: 2.5.1-dev
 
 description: Utility functions and classes related to the 'dart:async' library.
 homepage: https://www.github.com/dart-lang/async
diff --git a/test/cancelable_operation_test.dart b/test/cancelable_operation_test.dart
index 0e8d8d4..ebb8f49 100644
--- a/test/cancelable_operation_test.dart
+++ b/test/cancelable_operation_test.dart
@@ -195,6 +195,13 @@
       expect(() => completer.complete(1), throwsStateError);
     });
 
+    test('ignores completion errors after canceled', () async {
+      var completer = CancelableCompleter<int>();
+      completer.operation.value.whenComplete(expectAsync0(() {}, count: 0));
+      await completer.operation.cancel();
+      completer.complete(Future.error('error'));
+    });
+
     test('fires valueOrCancellation with the given value', () {
       var completer = CancelableCompleter();
       expect(completer.operation.valueOrCancellation(1), completion(equals(1)));
diff --git a/test/result/result_future_test.dart b/test/result/result_future_test.dart
index 7171005..d211dca 100644
--- a/test/result/result_future_test.dart
+++ b/test/result/result_future_test.dart
@@ -35,7 +35,7 @@
 
     // The completer calls its listeners asynchronously. We have to wait
     // before we can access the result.
-    return future.catchError((_) {}).then((_) {
+    return future.onError((_, __) {}).then((_) {
       var error = future.result!.asError!;
       expect(error.error, equals('error'));
       expect(error.stackTrace, equals(trace));
diff --git a/test/stream_sink_transformer_test.dart b/test/stream_sink_transformer_test.dart
index e5f6baa..20dda61 100644
--- a/test/stream_sink_transformer_test.dart
+++ b/test/stream_sink_transformer_test.dart
@@ -80,9 +80,9 @@
       // The futures shouldn't complete until the inner sink's close future
       // completes.
       var doneResult = ResultFuture(sink.done);
-      doneResult.catchError((_) {});
+      doneResult.onError((_, __) {});
       var closeResult = ResultFuture(sink.close());
-      closeResult.catchError((_) {});
+      closeResult.onError((_, __) {});
       await flushMicrotasks();
       expect(doneResult.isComplete, isFalse);
       expect(closeResult.isComplete, isFalse);
@@ -177,9 +177,9 @@
       // The futures shouldn't complete until the inner sink's close future
       // completes.
       var doneResult = ResultFuture(sink.done);
-      doneResult.catchError((_) {});
+      doneResult.onError((_, __) {});
       var closeResult = ResultFuture(sink.close());
-      closeResult.catchError((_) {});
+      closeResult.onError((_, __) {});
       await flushMicrotasks();
       expect(doneResult.isComplete, isFalse);
       expect(closeResult.isComplete, isFalse);