diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index 8a23d96e..84057e6a 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -87,7 +87,7 @@ impl AST {
         Self {
             source: None,
             #[cfg(feature = "metadata")]
-            doc: crate::SmartString::new_const(),
+            doc: None,
             body: (!stmt.is_empty()).then(|| stmt.into()),
             #[cfg(not(feature = "no_function"))]
             lib: functions.into(),