diff --git a/src/fn_call.rs b/src/fn_call.rs
index 539bb400..9ddf21bd 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -913,15 +913,14 @@ impl Engine {
                 let new_hash = FnCallHash::from_script(calc_fn_hash(empty(), fn_name, args_len));
                 // Arguments are passed as-is, adding the curried arguments
                 let mut curry = fn_ptr.curry().iter().cloned().collect::<StaticVec<_>>();
-                let mut arg_values = curry
+                let mut args = curry
                     .iter_mut()
                     .chain(call_args.iter_mut())
                     .collect::<StaticVec<_>>();
-                let args = arg_values.as_mut();
 
                 // Map it to name(args) in function-call style
                 self.exec_fn_call(
-                    mods, state, lib, fn_name, new_hash, args, false, false, pos, None, level,
+                    mods, state, lib, fn_name, new_hash, &mut args, false, false, pos, None, level,
                 )
             }
             KEYWORD_FN_PTR_CALL => {
@@ -952,15 +951,14 @@ impl Engine {
                 );
                 // Replace the first argument with the object pointer, adding the curried arguments
                 let mut curry = fn_ptr.curry().iter().cloned().collect::<StaticVec<_>>();
-                let mut arg_values = once(obj)
+                let mut args = once(obj)
                     .chain(curry.iter_mut())
                     .chain(call_args.iter_mut())
                     .collect::<StaticVec<_>>();
-                let args = arg_values.as_mut();
 
                 // Map it to name(args) in function-call style
                 self.exec_fn_call(
-                    mods, state, lib, fn_name, new_hash, args, is_ref, true, pos, None, level,
+                    mods, state, lib, fn_name, new_hash, &mut args, is_ref, true, pos, None, level,
                 )
             }
             KEYWORD_FN_PTR_CURRY => {
@@ -1030,13 +1028,12 @@ impl Engine {
                 };
 
                 // Attached object pointer in front of the arguments
-                let mut arg_values = once(obj)
+                let mut args = once(obj)
                     .chain(call_args.iter_mut())
                     .collect::<StaticVec<_>>();
-                let args = arg_values.as_mut();
 
                 self.exec_fn_call(
-                    mods, state, lib, fn_name, hash, args, is_ref, true, pos, None, level,
+                    mods, state, lib, fn_name, hash, &mut args, is_ref, true, pos, None, level,
                 )
             }
         }?;
@@ -1344,10 +1341,8 @@ impl Engine {
             }
         }
 
-        let args = args.as_mut();
-
         self.exec_fn_call(
-            mods, state, lib, name, hash, args, is_ref, false, pos, capture, level,
+            mods, state, lib, name, hash, &mut args, is_ref, false, pos, capture, level,
         )
         .map(|(v, _)| v)
     }
@@ -1468,7 +1463,6 @@ impl Engine {
                 if fn_def.body.is_empty() {
                     Ok(Dynamic::UNIT)
                 } else {
-                    let args = args.as_mut();
                     let new_scope = &mut Default::default();
 
                     let mut source = module.id_raw().cloned();
@@ -1477,7 +1471,7 @@ impl Engine {
                     let level = level + 1;
 
                     let result = self.call_script_fn(
-                        new_scope, mods, state, lib, &mut None, fn_def, args, pos, level,
+                        new_scope, mods, state, lib, &mut None, fn_def, &mut args, pos, level,
                     );
 
                     state.source = source;
@@ -1489,17 +1483,13 @@ impl Engine {
             Some(f) if f.is_plugin_fn() => f
                 .get_plugin_fn()
                 .clone()
-                .call(
-                    (self, fn_name, module.id(), &*mods, lib).into(),
-                    args.as_mut(),
-                )
+                .call((self, fn_name, module.id(), &*mods, lib).into(), &mut args)
                 .map_err(|err| err.fill_position(pos)),
 
-            Some(f) if f.is_native() => f.get_native_fn()(
-                (self, fn_name, module.id(), &*mods, lib).into(),
-                args.as_mut(),
-            )
-            .map_err(|err| err.fill_position(pos)),
+            Some(f) if f.is_native() => {
+                f.get_native_fn()((self, fn_name, module.id(), &*mods, lib).into(), &mut args)
+                    .map_err(|err| err.fill_position(pos))
+            }
 
             Some(f) => unreachable!("unknown function type: {:?}", f),
 
diff --git a/src/fn_native.rs b/src/fn_native.rs
index 8ff22a05..b98bf0ae 100644
--- a/src/fn_native.rs
+++ b/src/fn_native.rs
@@ -348,7 +348,7 @@ impl FnPtr {
             arg_values.iter_mut().collect()
         };
 
-        ctx.call_fn_dynamic_raw(self.fn_name(), is_method, args.as_mut())
+        ctx.call_fn_dynamic_raw(self.fn_name(), is_method, &mut args)
     }
 }
 
diff --git a/src/optimize.rs b/src/optimize.rs
index 2f3111bd..abb2dd35 100644
--- a/src/optimize.rs
+++ b/src/optimize.rs
@@ -947,7 +947,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
                     ""
                 };
 
-                if let Some(result) = call_fn_with_constant_arguments(&state, x.name.as_ref(), arg_values.as_mut())
+                if let Some(result) = call_fn_with_constant_arguments(&state, x.name.as_ref(), &mut arg_values)
                                         .or_else(|| {
                                             if !arg_for_type_of.is_empty() {
                                                 // Handle `type_of()`
diff --git a/src/parser.rs b/src/parser.rs
index 6169657c..a7024884 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -381,7 +381,7 @@ fn parse_fn_call(
             (Token::RightParen, _) => {
                 eat_token(input, Token::RightParen);
 
-                let hash = if let Some(modules) = namespace.as_mut() {
+                let hash = if let Some(ref mut modules) = namespace {
                     #[cfg(not(feature = "no_module"))]
                     modules.set_index(state.find_module(&modules[0].name));