diff --git a/nested/src/singleton/to_index.rs b/nested/src/singleton/to_index.rs
index 61f9337..85e919f 100644
--- a/nested/src/singleton/to_index.rs
+++ b/nested/src/singleton/to_index.rs
@@ -66,7 +66,7 @@ where
     type Item = SrcView::Item;
 
     fn area(&self) -> IndexArea<()> {
-        IndexArea::Full
+        IndexArea::Set(vec![ () ])
     }
 
     fn get(&self, _msg: &()) -> Option<Self::Item> {