diff --git a/Userland/Applications/Spreadsheet/ImportDialog.cpp b/Userland/Applications/Spreadsheet/ImportDialog.cpp
index d37a3c4722..bcf82d5122 100644
--- a/Userland/Applications/Spreadsheet/ImportDialog.cpp
+++ b/Userland/Applications/Spreadsheet/ImportDialog.cpp
@@ -177,7 +177,7 @@ void CSVImportDialogPage::update_preview()
     m_data_preview_table_view->update();
 }
 
-ErrorOr<Vector<NonnullRefPtr<Sheet>>, ByteString> ImportDialog::make_and_run_for(GUI::Window& parent, StringView mime, String const& filename, Core::File& file, Workbook& workbook)
+ErrorOr<Vector<NonnullRefPtr<Sheet>>, ByteString> ImportDialog::make_and_run_for(GUI::Window& parent, StringView mime, ByteString const& filename, Core::File& file, Workbook& workbook)
 {
     auto wizard = GUI::WizardDialog::create(&parent).release_value_but_fixme_should_propagate_errors();
     wizard->set_title("File Import Wizard");
@@ -247,7 +247,7 @@ ErrorOr<Vector<NonnullRefPtr<Sheet>>, ByteString> ImportDialog::make_and_run_for
     } else {
         auto page = GUI::WizardPage::create(
             "Import File Format"sv,
-            ByteString::formatted("Select the format you wish to import '{}' as", LexicalPath::basename(filename.to_byte_string())))
+            ByteString::formatted("Select the format you wish to import '{}' as", LexicalPath::basename(filename)))
                         .release_value_but_fixme_should_propagate_errors();
 
         page->on_next_page = [] { return nullptr; };
diff --git a/Userland/Applications/Spreadsheet/ImportDialog.h b/Userland/Applications/Spreadsheet/ImportDialog.h
index f9e6c00bcc..6d2286e09f 100644
--- a/Userland/Applications/Spreadsheet/ImportDialog.h
+++ b/Userland/Applications/Spreadsheet/ImportDialog.h
@@ -55,7 +55,7 @@ private:
 };
 
 struct ImportDialog {
-    static ErrorOr<Vector<NonnullRefPtr<Sheet>>, ByteString> make_and_run_for(GUI::Window& parent, StringView mime, String const& filename, Core::File& file, Workbook&);
+    static ErrorOr<Vector<NonnullRefPtr<Sheet>>, ByteString> make_and_run_for(GUI::Window& parent, StringView mime, ByteString const& filename, Core::File& file, Workbook&);
 };
 
 }
diff --git a/Userland/Applications/Spreadsheet/SpreadsheetWidget.cpp b/Userland/Applications/Spreadsheet/SpreadsheetWidget.cpp
index 1888b2544e..f5521360e0 100644
--- a/Userland/Applications/Spreadsheet/SpreadsheetWidget.cpp
+++ b/Userland/Applications/Spreadsheet/SpreadsheetWidget.cpp
@@ -136,7 +136,7 @@ SpreadsheetWidget::SpreadsheetWidget(GUI::Window& parent_window, Vector<NonnullR
         auto response = FileSystemAccessClient::Client::the().open_file(window(), options);
         if (response.is_error())
             return;
-        load_file(MUST(String::from_byte_string(response.value().filename())), response.value().stream());
+        load_file(response.value().filename(), response.value().stream());
     });
 
     m_import_action = GUI::Action::create("Import Sheets...", [&](auto&) {
@@ -150,7 +150,7 @@ SpreadsheetWidget::SpreadsheetWidget(GUI::Window& parent_window, Vector<NonnullR
         if (response.is_error())
             return;
 
-        import_sheets(MUST(String::from_byte_string(response.value().filename())), response.value().stream());
+        import_sheets(response.value().filename(), response.value().stream());
     });
 
     m_save_action = GUI::CommonActions::make_save_action([&](auto&) {
@@ -162,7 +162,7 @@ SpreadsheetWidget::SpreadsheetWidget(GUI::Window& parent_window, Vector<NonnullR
         auto response = FileSystemAccessClient::Client::the().request_file(window(), current_filename(), Core::File::OpenMode::Write);
         if (response.is_error())
             return;
-        save(MUST(String::from_byte_string(response.value().filename())), response.value().stream());
+        save(response.value().filename(), response.value().stream());
     });
 
     m_save_as_action = GUI::CommonActions::make_save_as_action([&](auto&) {
@@ -170,7 +170,7 @@ SpreadsheetWidget::SpreadsheetWidget(GUI::Window& parent_window, Vector<NonnullR
         auto response = FileSystemAccessClient::Client::the().save_file(window(), name, "sheets");
         if (response.is_error())
             return;
-        save(MUST(String::from_byte_string(response.value().filename())), response.value().stream());
+        save(response.value().filename(), response.value().stream());
         update_window_title();
     });
 
@@ -560,7 +560,7 @@ void SpreadsheetWidget::change_cell_static_color_format(Spreadsheet::FormatType
         apply_color_to_selected_cells(dialog->color());
 }
 
-void SpreadsheetWidget::save(String const& filename, Core::File& file)
+void SpreadsheetWidget::save(ByteString const& filename, Core::File& file)
 {
     auto result = m_workbook->write_to_file(filename, file);
     if (result.is_error()) {
@@ -569,10 +569,10 @@ void SpreadsheetWidget::save(String const& filename, Core::File& file)
     }
     undo_stack().set_current_unmodified();
     window()->set_modified(false);
-    GUI::Application::the()->set_most_recently_open_file(filename.to_byte_string());
+    GUI::Application::the()->set_most_recently_open_file(filename);
 }
 
-void SpreadsheetWidget::load_file(String const& filename, Core::File& file)
+void SpreadsheetWidget::load_file(ByteString const& filename, Core::File& file)
 {
     auto result = m_workbook->open_file(filename, file);
     if (result.is_error()) {
@@ -592,10 +592,10 @@ void SpreadsheetWidget::load_file(String const& filename, Core::File& file)
 
     setup_tabs(m_workbook->sheets());
     update_window_title();
-    GUI::Application::the()->set_most_recently_open_file(filename.to_byte_string());
+    GUI::Application::the()->set_most_recently_open_file(filename);
 }
 
-void SpreadsheetWidget::import_sheets(String const& filename, Core::File& file)
+void SpreadsheetWidget::import_sheets(ByteString const& filename, Core::File& file)
 {
     auto result = m_workbook->import_file(filename, file);
     if (result.is_error()) {
@@ -733,7 +733,7 @@ ErrorOr<void> SpreadsheetWidget::initialize_menubar(GUI::Window& window)
         auto response = FileSystemAccessClient::Client::the().request_file_read_only_approved(&window, action.text());
         if (response.is_error())
             return;
-        load_file(MUST(String::from_byte_string(response.value().filename())), response.value().stream());
+        load_file(response.value().filename(), response.value().stream());
     });
     file_menu->add_action(*m_quit_action);
 
diff --git a/Userland/Applications/Spreadsheet/SpreadsheetWidget.h b/Userland/Applications/Spreadsheet/SpreadsheetWidget.h
index d99ac857d2..bdffab1411 100644
--- a/Userland/Applications/Spreadsheet/SpreadsheetWidget.h
+++ b/Userland/Applications/Spreadsheet/SpreadsheetWidget.h
@@ -22,9 +22,9 @@ class SpreadsheetWidget final
 public:
     virtual ~SpreadsheetWidget() override = default;
 
-    void save(String const& filename, Core::File&);
-    void load_file(String const& filename, Core::File&);
-    void import_sheets(String const& filename, Core::File&);
+    void save(ByteString const& filename, Core::File&);
+    void load_file(ByteString const& filename, Core::File&);
+    void import_sheets(ByteString const& filename, Core::File&);
     bool request_close();
     void add_sheet();
     void add_sheet(NonnullRefPtr<Sheet>&&);
diff --git a/Userland/Applications/Spreadsheet/Workbook.cpp b/Userland/Applications/Spreadsheet/Workbook.cpp
index f2c8b40fe5..8c73611265 100644
--- a/Userland/Applications/Spreadsheet/Workbook.cpp
+++ b/Userland/Applications/Spreadsheet/Workbook.cpp
@@ -50,31 +50,31 @@ bool Workbook::set_filename(ByteString const& filename)
     return true;
 }
 
-ErrorOr<void, ByteString> Workbook::open_file(String const& filename, Core::File& file)
+ErrorOr<void, ByteString> Workbook::open_file(ByteString const& filename, Core::File& file)
 {
     auto mime = Core::guess_mime_type_based_on_filename(filename);
 
     // Make an import dialog, we might need to import it.
     m_sheets = TRY(ImportDialog::make_and_run_for(m_parent_window, mime, filename, file, *this));
 
-    set_filename(filename.to_byte_string());
+    set_filename(filename);
 
     return {};
 }
 
-ErrorOr<void> Workbook::write_to_file(String const& filename, Core::File& stream)
+ErrorOr<void> Workbook::write_to_file(ByteString const& filename, Core::File& stream)
 {
     auto mime = Core::guess_mime_type_based_on_filename(filename);
 
     // Make an export dialog, we might need to import it.
-    TRY(ExportDialog::make_and_run_for(mime, stream, filename.to_byte_string(), *this));
+    TRY(ExportDialog::make_and_run_for(mime, stream, filename, *this));
 
-    set_filename(filename.to_byte_string());
+    set_filename(filename);
     set_dirty(false);
     return {};
 }
 
-ErrorOr<bool, ByteString> Workbook::import_file(String const& filename, Core::File& file)
+ErrorOr<bool, ByteString> Workbook::import_file(ByteString const& filename, Core::File& file)
 {
     auto mime = Core::guess_mime_type_based_on_filename(filename);
 
diff --git a/Userland/Applications/Spreadsheet/Workbook.h b/Userland/Applications/Spreadsheet/Workbook.h
index 70dbb47d97..bf2d4706fe 100644
--- a/Userland/Applications/Spreadsheet/Workbook.h
+++ b/Userland/Applications/Spreadsheet/Workbook.h
@@ -15,10 +15,10 @@ class Workbook {
 public:
     Workbook(Vector<NonnullRefPtr<Sheet>>&& sheets, GUI::Window& parent_window);
 
-    ErrorOr<void, ByteString> open_file(String const& filename, Core::File&);
-    ErrorOr<void> write_to_file(String const& filename, Core::File&);
+    ErrorOr<void, ByteString> open_file(ByteString const& filename, Core::File&);
+    ErrorOr<void> write_to_file(ByteString const& filename, Core::File&);
 
-    ErrorOr<bool, ByteString> import_file(String const& filename, Core::File&);
+    ErrorOr<bool, ByteString> import_file(ByteString const& filename, Core::File&);
 
     ByteString const& current_filename() const { return m_current_filename; }
     bool set_filename(ByteString const& filename);
diff --git a/Userland/Applications/Spreadsheet/main.cpp b/Userland/Applications/Spreadsheet/main.cpp
index fbc345d84a..9f69f9426f 100644
--- a/Userland/Applications/Spreadsheet/main.cpp
+++ b/Userland/Applications/Spreadsheet/main.cpp
@@ -71,7 +71,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 
     if (!filename.is_empty()) {
         auto file = TRY(FileSystemAccessClient::Client::the().request_file_read_only_approved(window, filename));
-        spreadsheet_widget->load_file(TRY(String::from_byte_string(file.filename())), file.stream());
+        spreadsheet_widget->load_file(file.filename(), file.stream());
     }
 
     return app->exec();