diff --git a/build/ios/mojom/objc_templates/private_union_implementation.tmpl b/build/ios/mojom/objc_templates/private_union_implementation.tmpl
index 29a47f6266d..68515db6c27 100644
--- a/build/ios/mojom/objc_templates/private_union_implementation.tmpl
+++ b/build/ios/mojom/objc_templates/private_union_implementation.tmpl
@@ -100,7 +100,7 @@
 
 - ({{cpp_namespace}}::{{union.name}}Ptr)cppObjPtr
 {
-  auto obj = {{cpp_namespace}}::{{union.name}}Ptr(std::in_place);
+  {{cpp_namespace}}::{{union.name}}Ptr obj;
   switch (self.tag) {
     case {{tag_enum_name}}Null: {
       break;
@@ -108,7 +108,7 @@
 {%- for field in union.fields %}
 {%-   set field_tag = "%s%s"|format(tag_enum_name, field.name|objc_enum_formatter) %}
     case {{field_tag}}: {
-      obj->set_{{field.name}}({{field|objc_to_cpp_assign('self')}});
+      obj = {{cpp_namespace}}::{{union.name}}::New{{field.name|under_to_camel}}({{field|objc_to_cpp_assign('self')}});
       break;
     }
 {%- endfor %}
diff --git a/mojo/brave_ast_patcher/brave_ast_patcher_unittest.cc b/mojo/brave_ast_patcher/brave_ast_patcher_unittest.cc
index 2010eddff4f..4530f496bc8 100644
--- a/mojo/brave_ast_patcher/brave_ast_patcher_unittest.cc
+++ b/mojo/brave_ast_patcher/brave_ast_patcher_unittest.cc
@@ -60,9 +60,8 @@ TEST(BraveAstPatcherTest, OriginalTypes) {
   EXPECT_EQ(global_struct.nested_enum_member,
             GlobalStruct::NestedEnum::VALUE_NESTED_CONSTANT);
 
-  GlobalUnion global_union;
-  global_union.set_bool_value(false);
-  global_union.set_string_value(std::string());
+  auto global_union = GlobalUnion::NewBoolValue(false);
+  global_union->set_string_value(std::string());
 
   EXPECT_EQ(static_cast<int>(GlobalInterface::NestedEnum::VALUE), 0);
   EXPECT_EQ(
@@ -89,9 +88,8 @@ TEST(BraveAstPatcherTest, NewTypes) {
   new_global_struct.new_global_enum_member = NewGlobalEnum::VALUE;
   new_global_struct.nested_enum_member = NewGlobalStruct::NestedEnum::VALUE;
 
-  NewGlobalUnion new_global_union;
-  new_global_union.set_int32_value(0);
-  new_global_union.set_float_value(0.0f);
+  auto new_global_union = NewGlobalUnion::NewInt32Value(0);
+  new_global_union->set_float_value(0.0f);
 
   EXPECT_EQ(static_cast<int>(NewGlobalInterface::NestedEnum::VALUE), 0);
   EXPECT_EQ(
@@ -123,9 +121,8 @@ TEST(BraveAstPatcherTest, ExtendedTypes) {
   EXPECT_EQ(global_struct.new_nested_enum_member,
             GlobalStruct::NewNestedEnum::VALUE_NESTED_CONSTANT);
 
-  GlobalUnion global_union;
-  global_union.set_int32_value(0);
-  global_union.set_float_value(0.0f);
+  auto global_union = GlobalUnion::NewInt32Value(0);
+  global_union->set_float_value(0.0f);
 
   EXPECT_EQ(static_cast<int>(GlobalInterface::NestedEnum::NEW_VALUE), 1);
   EXPECT_EQ(