diff --git a/pkg/vm/lib/transformations/type_flow/transformer.dart b/pkg/vm/lib/transformations/type_flow/transformer.dart
index e781924ed2d..d0907745437 100644
--- a/pkg/vm/lib/transformations/type_flow/transformer.dart
+++ b/pkg/vm/lib/transformations/type_flow/transformer.dart
@@ -731,24 +731,22 @@ class AnnotateKernel extends RecursiveVisitor {
         _setUnreachable(member);
       }
 
-      if (member is! Field) {
-        final unboxingInfoMetadata = _unboxingInfo.getUnboxingInfoOfMember(
-          member,
-        );
-        if (unboxingInfoMetadata != null) {
-          // Check for partitions that only have abstract methods should be marked as boxed.
-          if (unboxingInfoMetadata.returnInfo == UnboxingType.kUnknown) {
-            unboxingInfoMetadata.returnInfo = UnboxingType.kBoxed;
-          }
-          for (int i = 0; i < unboxingInfoMetadata.argsInfo.length; i++) {
-            if (unboxingInfoMetadata.argsInfo[i] == UnboxingType.kUnknown) {
-              unboxingInfoMetadata.argsInfo[i] = UnboxingType.kBoxed;
-            }
-          }
-          if (!unboxingInfoMetadata.isTrivial) {
-            _unboxingInfoMetadata.mapping[member] = unboxingInfoMetadata;
+      final unboxingInfoMetadata = _unboxingInfo.getUnboxingInfoOfMember(
+        member,
+      );
+      if (unboxingInfoMetadata != null) {
+        // Check for partitions that only have abstract methods should be marked as boxed.
+        if (unboxingInfoMetadata.returnInfo == UnboxingType.kUnknown) {
+          unboxingInfoMetadata.returnInfo = UnboxingType.kBoxed;
+        }
+        for (int i = 0; i < unboxingInfoMetadata.argsInfo.length; i++) {
+          if (unboxingInfoMetadata.argsInfo[i] == UnboxingType.kUnknown) {
+            unboxingInfoMetadata.argsInfo[i] = UnboxingType.kBoxed;
           }
         }
+        if (!unboxingInfoMetadata.isTrivial) {
+          _unboxingInfoMetadata.mapping[member] = unboxingInfoMetadata;
+        }
       }
     }
 
diff --git a/pkg/vm/testcases/transformations/type_flow/transformer/regress_b404559785.dart.expect b/pkg/vm/testcases/transformations/type_flow/transformer/regress_b404559785.dart.expect
index 72bb8823880..cb00e68e846 100644
--- a/pkg/vm/testcases/transformations/type_flow/transformer/regress_b404559785.dart.expect
+++ b/pkg/vm/testcases/transformations/type_flow/transformer/regress_b404559785.dart.expect
@@ -6,6 +6,7 @@ abstract class Foo extends core::Object {
 
   [@vm.unreachable.metadata=]
   [@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasNonThisUses:false,hasTearOffUses:false,getterSelectorId:1]
+  [@vm.unboxing-info.metadata=[!regcc]]
   @#C3
   late final field core::int hashCode = throw "Attempt to execute code removed by Dart AOT compiler (TFA)";
 }
diff --git a/runtime/tests/vm/dart/regress_b_450678575_test.dart b/runtime/tests/vm/dart/regress_b_450678575_test.dart
new file mode 100644
index 00000000000..3cb8b9322e9
--- /dev/null
+++ b/runtime/tests/vm/dart/regress_b_450678575_test.dart
@@ -0,0 +1,65 @@
+// Copyright (c) 2025, 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 b/450678575.
+//
+// Verifies that compiler uses correct calling conventions (!regcc)
+// when using unreachable field as an interface target.
+
+import 'package:expect/expect.dart';
+
+bool opaqueTrue = int.parse('1') == 1;
+
+int listener = -1;
+
+abstract class ChangeNotifier {
+  void addListener();
+}
+
+class Notifier1 implements ChangeNotifier {
+  @pragma('vm:never-inline')
+  void addListener() {
+    listener = 1;
+  }
+}
+
+class Notifier2 implements ChangeNotifier {
+  @pragma('vm:never-inline')
+  void addListener() {
+    listener = 2;
+  }
+}
+
+abstract class M {
+  // This field is unreachable and only serves as
+  // an interface target.
+  @pragma("vm:entry-point")
+  final ChangeNotifier accessibilityFocus = Notifier2();
+}
+
+class B implements M {
+  @pragma("vm:entry-point")
+  final ChangeNotifier accessibilityFocus = Notifier1();
+}
+
+class C implements M {
+  @pragma("vm:entry-point")
+  final ChangeNotifier accessibilityFocus = Notifier2();
+}
+
+// Clobber values on top of the stack.
+@pragma('vm:never-inline')
+@pragma("vm:entry-point")
+void boxed(int a, int b) {
+  print(a);
+  print(b);
+}
+
+M instance = opaqueTrue ? B() : C();
+
+void main(List<String> args) {
+  boxed(1, 2);
+  instance.accessibilityFocus.addListener();
+  Expect.equals(1, listener);
+}