diff --git a/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp b/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp
index 4c5c8d4989..9de6d960ac 100644
--- a/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp
+++ b/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp
@@ -1145,6 +1145,10 @@ static void generate_to_cpp(SourceGenerator& generator, ParameterType& parameter
                         VERIFY(dictionary_type);
                         union_generator.append(R"~~~(
     @union_type@ @cpp_name@ = @js_name@@js_suffix@.is_undefined() ? TRY(@js_name@@js_suffix@_to_dictionary(@js_name@@js_suffix@)) : TRY(@js_name@@js_suffix@_to_variant(@js_name@@js_suffix@));
+)~~~");
+                    } else if (optional_default_value->to_int().has_value() || optional_default_value->to_uint().has_value()) {
+                        union_generator.append(R"~~~(
+    @union_type@ @cpp_name@ = @js_name@@js_suffix@.is_undefined() ? @parameter.optional_default_value@ : TRY(@js_name@@js_suffix@_to_variant(@js_name@@js_suffix@));
 )~~~");
                     } else {
                         TODO();