diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1560001..4680638 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
-## 2.6.2
+## 2.6.2-dev
 
-* Internal changes only.
+* Fix a bug where `CancelableOperation.then` may invoke the `onValue` callback,
+  even if it had been canceled before `CancelableOperation.value` completes.
 
 ## 2.6.1
 
diff --git a/lib/src/cancelable_operation.dart b/lib/src/cancelable_operation.dart
index c321078..6e6ef17 100644
--- a/lib/src/cancelable_operation.dart
+++ b/lib/src/cancelable_operation.dart
@@ -101,7 +101,7 @@
 
     valueOrCancellation().then((T? result) {
       if (!completer.isCanceled) {
-        if (isCompleted) {
+        if (isCompleted && !isCanceled) {
           assert(result is T);
           completer.complete(Future.sync(() => onValue(result as T)));
         } else if (onCancel != null) {
diff --git a/test/cancelable_operation_test.dart b/test/cancelable_operation_test.dart
index 0e8d8d4..47a1e91 100644
--- a/test/cancelable_operation_test.dart
+++ b/test/cancelable_operation_test.dart
@@ -267,10 +267,10 @@
       onError = expectAsync2((e, s) => 'Fake', count: 0, id: 'onError');
       onCancel = expectAsync0(() => 'Fake', count: 0, id: 'onCancel');
       propagateCancel = false;
+      originalCompleter = CancelableCompleter();
     });
 
     CancelableOperation<String> runThen() {
-      originalCompleter = CancelableCompleter();
       return originalCompleter.operation.then(onValue!,
           onError: onError,
           onCancel: onCancel,
@@ -387,6 +387,29 @@
         expect(runThen().value, throwsA('error'));
         originalCompleter.operation.cancel();
       });
+
+      test('after completing with a future does not invoke `onValue`',
+          () async {
+        onValue = expectAsync1((_) => '', count: 0);
+        onCancel = null;
+        var operation = runThen();
+        var workCompleter = Completer<int>();
+        originalCompleter.complete(workCompleter.future);
+        originalCompleter.operation.cancel();
+        workCompleter.complete(0);
+        expect(operation.isCanceled, true);
+        await workCompleter.future;
+      });
+
+      test('after the value is completed invokes `onValue`', () {
+        onValue = expectAsync1((_) => 'foo', count: 1);
+        onCancel = expectAsync1((_) => '', count: 0);
+        originalCompleter.complete(0);
+        originalCompleter.operation.cancel();
+        var operation = runThen();
+        expect(operation.value, completion('foo'));
+        expect(operation.isCanceled, false);
+      });
     });
 
     group('returned operation canceled', () {