diff --git a/crates/nu-parser/src/flatten.rs b/crates/nu-parser/src/flatten.rs
index 8411025272..6a12f8484a 100644
--- a/crates/nu-parser/src/flatten.rs
+++ b/crates/nu-parser/src/flatten.rs
@@ -329,6 +329,9 @@ fn flatten_expression_into(
             if let Expr::String(..) | Expr::GlobPattern(..) = &head.expr {
                 output.push((
                     head.span,
+                    // If this external call is through an alias, then head.span points to the
+                    // name of the alias, but we also need the name of the aliased command. We
+                    // recover this from the span referenced by head.span_id.
                     FlatShape::External(working_set.get_span(head.span_id)),
                 ));
             } else {