diff --git a/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp b/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp
index e009eb0f7f..5f1d32e6e2 100644
--- a/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp
+++ b/Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator/IDLGenerators.cpp
@@ -1334,7 +1334,7 @@ static void generate_to_cpp(SourceGenerator& generator, ParameterType& parameter
                 if (!optional_default_value.has_value() || optional_default_value == "null"sv) {
                     union_generator.append(R"~~~(
     Optional<@union_type@> @cpp_name@;
-    if (!@js_name@@js_suffix@.is_undefined())
+    if (!@js_name@@js_suffix@.is_nullish())
         @cpp_name@ = TRY(@js_name@@js_suffix@_to_variant(@js_name@@js_suffix@));
 )~~~");
                 } else {