diff --git a/pkg/vm/lib/transformations/type_flow/unboxing_info.dart b/pkg/vm/lib/transformations/type_flow/unboxing_info.dart
index a528575bbc0..4325bb95c51 100644
--- a/pkg/vm/lib/transformations/type_flow/unboxing_info.dart
+++ b/pkg/vm/lib/transformations/type_flow/unboxing_info.dart
@@ -194,7 +194,7 @@ class UnboxingInfoManager {
         // Arguments of implicit setters for covariant fields
         // cannot be unboxed based on the field type as setter
         // performs a type check before value is assigned to the field.
-        if (member.isCovariantByDeclaration) {
+        if (member.isCovariantByDeclaration || member.isCovariantByClass) {
           unboxingInfo.argsInfo.length = 0;
         } else {
           _applyToArg(member, unboxingInfo, 0, inferredType);
diff --git a/runtime/tests/vm/dart/regress_63419_test.dart b/runtime/tests/vm/dart/regress_63419_test.dart
new file mode 100644
index 00000000000..f13f2908faf
--- /dev/null
+++ b/runtime/tests/vm/dart/regress_63419_test.dart
@@ -0,0 +1,45 @@
+// Copyright (c) 2026, 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.
+
+// Regression test for https://github.com/dart-lang/sdk/issues/63419.
+
+// VMOptions=--compiler-passes=-Inlining
+
+import 'package:expect/expect.dart';
+
+abstract interface class Box1<T> {
+  T get x;
+  void set x(T value);
+}
+
+class StringBox implements Box1<String> {
+  @pragma("vm:never-inline")
+  String x = 'yay';
+}
+
+abstract interface class Box2<T> {
+  T get x;
+  void set x(T value);
+}
+
+class IntBox implements Box2<int> {
+  @pragma("vm:never-inline")
+  int x = 0;
+}
+
+void main() {
+  final Box1<Object> box1 = StringBox();
+  box1.x = 'xyz';
+  Expect.equals('xyz', box1.x);
+  Expect.throws(() {
+    box1.x = 123;
+  });
+
+  final Box2<Object> box2 = IntBox();
+  box2.x = 123;
+  Expect.equals(123, box2.x);
+  Expect.throws(() {
+    box2.x = 'abc';
+  });
+}
diff --git a/runtime/vm/compiler/frontend/scope_builder.cc b/runtime/vm/compiler/frontend/scope_builder.cc
index 862d927c49d..116a4ba8580 100644
--- a/runtime/vm/compiler/frontend/scope_builder.cc
+++ b/runtime/vm/compiler/frontend/scope_builder.cc
@@ -308,7 +308,8 @@ ScopeBuildingResult* ScopeBuilder::BuildScopes() {
               AbstractType::ZoneHandle(Z, function.ParameterTypeAt(pos)),
               LocalVariable::kNoKernelOffset, /*is_late=*/false,
               /*inferred_type_md=*/nullptr,
-              /*inferred_arg_type_md=*/field.is_covariant()
+              /*inferred_arg_type_md=*/
+              (field.is_covariant() || field.is_generic_covariant_impl())
                   ? nullptr
                   : &inferred_field_type);
         } else {