diff --git a/Userland/Libraries/LibWeb/HTML/FormControlInfrastructure.cpp b/Userland/Libraries/LibWeb/HTML/FormControlInfrastructure.cpp
index c261bb2be2b..bd28b553aa2 100644
--- a/Userland/Libraries/LibWeb/HTML/FormControlInfrastructure.cpp
+++ b/Userland/Libraries/LibWeb/HTML/FormControlInfrastructure.cpp
@@ -164,7 +164,7 @@ WebIDL::ExceptionOr<Optional<Vector<XHR::FormDataEntry>>> construct_entry_list(J
     // 7. Fire an event named formdata at form using FormDataEvent, with the formData attribute initialized to form data and the bubbles attribute initialized to true.
     FormDataEventInit init {};
     init.form_data = form_data;
-    auto form_data_event = TRY(FormDataEvent::construct_impl(realm, HTML::EventNames::formdata, init));
+    auto form_data_event = TRY(FormDataEvent::construct_impl(realm, String::from_deprecated_string(HTML::EventNames::formdata).release_value_but_fixme_should_propagate_errors(), init));
     form_data_event->set_bubbles(true);
     form.dispatch_event(form_data_event);
 
diff --git a/Userland/Libraries/LibWeb/HTML/FormDataEvent.cpp b/Userland/Libraries/LibWeb/HTML/FormDataEvent.cpp
index aa5fa25f11f..1337970c231 100644
--- a/Userland/Libraries/LibWeb/HTML/FormDataEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/FormDataEvent.cpp
@@ -10,13 +10,13 @@
 
 namespace Web::HTML {
 
-WebIDL::ExceptionOr<JS::NonnullGCPtr<FormDataEvent>> FormDataEvent::construct_impl(JS::Realm& realm, DeprecatedString const& event_name, FormDataEventInit const& event_init)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<FormDataEvent>> FormDataEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, FormDataEventInit const& event_init)
 {
     return MUST_OR_THROW_OOM(realm.heap().allocate<FormDataEvent>(realm, realm, event_name, event_init));
 }
 
-FormDataEvent::FormDataEvent(JS::Realm& realm, DeprecatedString const& event_name, FormDataEventInit const& event_init)
-    : DOM::Event(realm, event_name, event_init)
+FormDataEvent::FormDataEvent(JS::Realm& realm, FlyString const& event_name, FormDataEventInit const& event_init)
+    : DOM::Event(realm, event_name.to_deprecated_fly_string(), event_init)
     , m_form_data(event_init.form_data)
 {
 }
diff --git a/Userland/Libraries/LibWeb/HTML/FormDataEvent.h b/Userland/Libraries/LibWeb/HTML/FormDataEvent.h
index 3c2a4254e2f..cd32e213110 100644
--- a/Userland/Libraries/LibWeb/HTML/FormDataEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/FormDataEvent.h
@@ -19,14 +19,14 @@ class FormDataEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(FormDataEvent, DOM::Event);
 
 public:
-    static WebIDL::ExceptionOr<JS::NonnullGCPtr<FormDataEvent>> construct_impl(JS::Realm&, DeprecatedString const& event_name, FormDataEventInit const& event_init);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<FormDataEvent>> construct_impl(JS::Realm&, FlyString const& event_name, FormDataEventInit const& event_init);
 
     virtual ~FormDataEvent() override;
 
     JS::GCPtr<XHR::FormData> form_data() const { return m_form_data; }
 
 private:
-    FormDataEvent(JS::Realm&, DeprecatedString const& event_name, FormDataEventInit const& event_init);
+    FormDataEvent(JS::Realm&, FlyString const& event_name, FormDataEventInit const& event_init);
 
     JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
 
diff --git a/Userland/Libraries/LibWeb/HTML/FormDataEvent.idl b/Userland/Libraries/LibWeb/HTML/FormDataEvent.idl
index 3b198d7658a..d21e8116d39 100644
--- a/Userland/Libraries/LibWeb/HTML/FormDataEvent.idl
+++ b/Userland/Libraries/LibWeb/HTML/FormDataEvent.idl
@@ -2,7 +2,7 @@
 #import <XHR/FormData.idl>
 
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#the-formdataevent-interface
-[Exposed=Window]
+[Exposed=Window, UseNewAKString]
 interface FormDataEvent : Event {
     constructor(DOMString type, FormDataEventInit eventInitDict);