diff --git a/src/protocol/ast.rs b/src/protocol/ast.rs
index 83ae094fbfd5a4aad116353aef5f60c9c8c6c1f5..95195aef473b46c535fb2b034a712da10bf953ca 100644
--- a/src/protocol/ast.rs
+++ b/src/protocol/ast.rs
@@ -1647,6 +1647,12 @@ pub struct SlicingExpression {
     pub unique_id_in_definition: i32,
 }
 
+#[derive(Debug, Clone)]
+pub enum SelectKind {
+    StructField(Identifier),
+    TupleMember(u64), // u64 is overkill, but space is taken up by `StructField` variant anyway
+}
+
 #[derive(Debug, Clone)]
 pub struct SelectExpression {
     pub this: SelectExpressionId,
@@ -1654,7 +1660,7 @@ pub struct SelectExpression {
     pub operator_span: InputSpan, // of the '.'
     pub full_span: InputSpan, // includes subject and field
     pub subject: ExpressionId,
-    pub field_name: Identifier,
+    pub kind: SelectKind,
     // Validator/Linker
     pub parent: ExpressionParent,
     pub unique_id_in_definition: i32,