diff --git a/src/ast.rs b/src/ast.rs
index 15eb1606d..a782ece6c 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -269,6 +269,7 @@ fn as_job_list(&self) -> Option<&JobList> {
     }
 }
 
+#[allow(unused)]
 trait ConcreteNodeMut {
     // Cast to any sub-trait.
     fn as_mut_leaf(&mut self) -> Option<&mut dyn Leaf> {