diff --git a/src/ast.rs b/src/ast.rs
index 48ccb3bc..94281968 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -780,6 +780,7 @@ impl AST {
     /// let mut iter = ast.iter_literal_variables(true, false)
     ///                   .map(|(name, is_const, value)| (name, is_const, value.as_int().unwrap()));
     ///
+    /// # #[cfg(not(feature = "no_optimize"))]
     /// assert_eq!(iter.next(), Some(("A", true, 42)));
     /// assert_eq!(iter.next(), Some(("C", true, 999)));
     /// assert_eq!(iter.next(), None);
@@ -793,6 +794,7 @@ impl AST {
     /// let mut iter = ast.iter_literal_variables(true, true)
     ///                   .map(|(name, is_const, value)| (name, is_const, value.as_int().unwrap()));
     ///
+    /// # #[cfg(not(feature = "no_optimize"))]
     /// assert_eq!(iter.next(), Some(("A", true, 42)));
     /// assert_eq!(iter.next(), Some(("b", false, 123)));
     /// assert_eq!(iter.next(), Some(("C", true, 999)));
diff --git a/src/engine_api.rs b/src/engine_api.rs
index c065b073..49595865 100644
--- a/src/engine_api.rs
+++ b/src/engine_api.rs
@@ -2070,9 +2070,11 @@ impl Engine {
     pub fn optimize_ast(
         &self,
         scope: &Scope,
-        mut ast: AST,
+        ast: AST,
         optimization_level: crate::OptimizationLevel,
     ) -> AST {
+        let mut ast = ast;
+
         #[cfg(not(feature = "no_function"))]
         let lib = ast
             .lib()