diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 625bcd4ec9c3..42afe892de92 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -385,6 +385,7 @@ pub type stmt = spanned<stmt_>;
 
 #[deriving(Eq, Encodable, Decodable)]
 pub enum stmt_ {
+    // could be an item or a local (let) binding:
     stmt_decl(@decl, node_id),
 
     // expr without trailing semi-colon (must have unit type):
@@ -414,7 +415,9 @@ pub type decl = spanned<decl_>;
 
 #[deriving(Eq, Encodable, Decodable)]
 pub enum decl_ {
+    // a local (let) binding:
     decl_local(@local),
+    // an item binding:
     decl_item(@item),
 }