diff --git a/runtime/tests/vm/dart/regress_flutter63819_test.dart b/runtime/tests/vm/dart/regress_flutter63819_test.dart
new file mode 100644
index 00000000000..56d24122d67
--- /dev/null
+++ b/runtime/tests/vm/dart/regress_flutter63819_test.dart
@@ -0,0 +1,31 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Verify that 'is' test of a nullable type accepts null.
+// Regression test for https://github.com/flutter/flutter/issues/63819.
+
+import 'package:expect/expect.dart';
+
+abstract class A {}
+
+class B extends A {}
+
+class C extends A {}
+
+@pragma('vm:never-inline')
+bool foo(A? x) {
+  if (x is C?) {
+    print('$x is C?');
+    return true;
+  }
+  print('$x is not C?');
+  return false;
+}
+
+void main() {
+  B();
+  C();
+  Expect.isFalse(foo(B()));
+  Expect.isTrue(foo(null));
+}
diff --git a/runtime/vm/compiler/backend/il.cc b/runtime/vm/compiler/backend/il.cc
index d066f1193e7..5f51a5b384c 100644
--- a/runtime/vm/compiler/backend/il.cc
+++ b/runtime/vm/compiler/backend/il.cc
@@ -453,6 +453,12 @@ bool HierarchyInfo::InstanceOfHasClassRange(const AbstractType& type,
                                             intptr_t* lower_limit,
                                             intptr_t* upper_limit) {
   ASSERT(CompilerState::Current().is_aot());
+  if (type.IsNullable()) {
+    // 'is' test for nullable types should accept null cid in addition to the
+    // class range. In most cases it is not possible to extend class range to
+    // include kNullCid.
+    return false;
+  }
   if (CanUseSubtypeRangeCheckFor(type)) {
     const Class& type_class =
         Class::Handle(thread()->zone(), type.type_class());