diff --git a/ablescript/src/variables.rs b/ablescript/src/variables.rs
index e9dec5b..66c3ffc 100644
--- a/ablescript/src/variables.rs
+++ b/ablescript/src/variables.rs
@@ -838,7 +838,13 @@ impl ops::Not for Value {
 
                     Functio::Able { params, body }
                 }
-                Functio::Builtin(_) => todo!(),
+                Functio::Builtin(b) => {
+                    let arity = b.arity;
+                    Functio::Builtin(BuiltinFunctio::new(
+                        move |args| b.call(&args.iter().cloned().rev().collect::<Vec<_>>()),
+                        arity,
+                    ))
+                }
                 Functio::Chain { functios, kind } => {
                     let (a, b) = *functios;
                     Functio::Chain {