diff --git a/lib/types/theme-types.js b/lib/types/theme-types.js
--- a/lib/types/theme-types.js
+++ b/lib/types/theme-types.js
@@ -16,4 +16,4 @@
   // revert to `preference: osCanTheme ? 'system' : 'light'`
   // to re-enable theming
   preference: 'dark',
-};
+} as const;