diff --git a/godot-codegen/src/conv/type_conversions.rs b/godot-codegen/src/conv/type_conversions.rs
index d87fc7b84..e9f25465b 100644
--- a/godot-codegen/src/conv/type_conversions.rs
+++ b/godot-codegen/src/conv/type_conversions.rs
@@ -236,8 +236,8 @@ fn to_rust_type_uncached(full_ty: &GodotTy, ctx: &mut Context) -> RustTy {
 
         RustTy::EngineClass {
             tokens: quote! { Gd<#qualified_class> },
-            arg_view: quote! { ObjectArg<#qualified_class> },
-            impl_as_arg: quote! { impl AsObjectArg<#qualified_class> },
+            object_arg: quote! { ObjectArg<#qualified_class> },
+            impl_as_object_arg: quote! { impl AsObjectArg<#qualified_class> },
             inner_class: ty,
         }
     }
@@ -266,7 +266,7 @@ fn to_rust_expr_inner(expr: &str, ty: &RustTy, is_inner: bool) -> TokenStream {
             return match ty {
                 RustTy::BuiltinIdent(ident) if ident == "Variant" => quote! { Variant::nil() },
                 RustTy::EngineClass { .. } => {
-                    quote! { ObjectArg::null() }
+                    quote! { Gd::null_arg() }
                 }
                 _ => panic!("null not representable in target type {ty:?}"),
             }
diff --git a/godot-codegen/src/generator/default_parameters.rs b/godot-codegen/src/generator/default_parameters.rs
index 7012af66f..6bc6d3976 100644
--- a/godot-codegen/src/generator/default_parameters.rs
+++ b/godot-codegen/src/generator/default_parameters.rs
@@ -247,30 +247,33 @@ fn make_extender(
             default_value,
         } = param;
 
-        let type_ = type_.param_decl();
+        let (field_type, needs_conversion) = type_.private_field_decl();
 
         // Initialize with default parameters where available, forward constructor args otherwise
         let init = if let Some(value) = default_value {
-            quote! { #name: #value }
+            make_field_init(name, value, needs_conversion)
         } else {
             quote! { #name }
         };
 
-        result.builder_fields.push(quote! { #name: #type_ });
+        result.builder_fields.push(quote! { #name: #field_type });
         result.builder_args.push(quote! { self.#name });
         result.builder_inits.push(init);
     }
 
     for param in default_fn_params {
         let FnParam { name, type_, .. } = param;
-        let type_ = type_.param_decl();
+        let param_type = type_.param_decl();
+        let (_, field_needs_conversion) = type_.private_field_decl();
+
+        let field_init = make_field_init(name, &quote! { value }, field_needs_conversion);
 
         let method = quote! {
             #[inline]
-            pub fn #name(self, value: #type_) -> Self {
+            pub fn #name(self, value: #param_type) -> Self {
                 // Currently not testing whether the parameter was already set
                 Self {
-                    #name: value,
+                    #field_init,
                     ..self
                 }
             }
@@ -281,3 +284,11 @@ fn make_extender(
 
     result
 }
+
+fn make_field_init(name: &Ident, expr: &TokenStream, needs_conversion: bool) -> TokenStream {
+    if needs_conversion {
+        quote! { #name: #expr.as_object_arg() }
+    } else {
+        quote! { #name: #expr }
+    }
+}
diff --git a/godot-codegen/src/generator/functions_common.rs b/godot-codegen/src/generator/functions_common.rs
index 85fac7263..a052de160 100644
--- a/godot-codegen/src/generator/functions_common.rs
+++ b/godot-codegen/src/generator/functions_common.rs
@@ -320,8 +320,8 @@ pub(crate) fn make_params_exprs<'a>(
         // Objects (Gd<T>) use implicit conversions via AsObjectArg. Only use in non-virtual functions.
         match &param.type_ {
             RustTy::EngineClass {
-                arg_view,
-                impl_as_arg,
+                object_arg: arg_view,
+                impl_as_object_arg: impl_as_arg,
                 ..
             } if !is_virtual => {
                 // Parameter declarations in signature: impl AsObjectArg<T>
diff --git a/godot-codegen/src/models/domain.rs b/godot-codegen/src/models/domain.rs
index 373cfc71f..51918de85 100644
--- a/godot-codegen/src/models/domain.rs
+++ b/godot-codegen/src/models/domain.rs
@@ -621,10 +621,10 @@ pub enum RustTy {
         tokens: TokenStream,
 
         /// Tokens with `ObjectArg<T>` (used in `type CallSig` tuple types).
-        arg_view: TokenStream,
+        object_arg: TokenStream,
 
         /// Signature declaration with `impl AsObjectArg<T>`.
-        impl_as_arg: TokenStream,
+        impl_as_object_arg: TokenStream,
 
         /// only inner `T`
         #[allow(dead_code)] // only read in minimal config
@@ -639,12 +639,20 @@ impl RustTy {
     pub fn param_decl(&self) -> TokenStream {
         match self {
             RustTy::EngineClass {
-                arg_view: raw_gd, ..
-            } => raw_gd.clone(),
+                impl_as_object_arg, ..
+            } => impl_as_object_arg.clone(),
             other => other.to_token_stream(),
         }
     }
 
+    /// Returns `( <field tokens>, <needs .as_object_arg()> )`.
+    pub fn private_field_decl(&self) -> (TokenStream, bool) {
+        match self {
+            RustTy::EngineClass { object_arg, .. } => (object_arg.clone(), true),
+            other => (other.to_token_stream(), false),
+        }
+    }
+
     pub fn return_decl(&self) -> TokenStream {
         match self {
             Self::EngineClass { tokens, .. } => quote! { -> Option<#tokens> },