diff --git a/kitty/boss.py b/kitty/boss.py
index 6435210e7..67fce663c 100644
--- a/kitty/boss.py
+++ b/kitty/boss.py
@@ -2698,6 +2698,7 @@ def apply_new_options(self, opts: Options) -> None:
         if theme_colors.has_applied_theme:
             theme_colors.refresh()
             if theme_colors.has_applied_theme:  # in case the theme file was deleted
+                assert theme_colors.applied_theme  # to make mypy happy
                 theme_colors.apply_theme(theme_colors.applied_theme, notify_on_bg_change=False)
         for w in self.all_windows:
             if w.screen.color_profile.default_bg != bg_colors_before.get(w.id):