diff --git a/src/module.ts b/src/module.ts
index 41142c9fc..69d2ba272 100644
--- a/src/module.ts
+++ b/src/module.ts
@@ -297,7 +297,7 @@ declare module '#app' {
         initialSetup: boolean
         context: Context
       }
-    ) => MaybePromise<void>
+    ) => MaybePromise<string | void>
     'i18n:localeSwitched': (params: LocaleSwitch) => MaybePromise<void>
   }
 }