diff --git a/pyo3-macros-backend/src/module.rs b/pyo3-macros-backend/src/module.rs
index 9def7b481d8..baec0f20c44 100644
--- a/pyo3-macros-backend/src/module.rs
+++ b/pyo3-macros-backend/src/module.rs
@@ -150,7 +150,7 @@ pub fn add_fn_to_module(
             syn::FnArg::Receiver(_) => {
                 bail_spanned!(input.span() => "unexpected receiver for #[pyfn]");
             }
-            syn::FnArg::Typed(ref mut cap) => {
+            syn::FnArg::Typed(cap) => {
                 if pyfn_attrs.pass_module && i == 0 {
                     if let syn::Type::Reference(tyref) = cap.ty.as_ref() {
                         if let syn::Type::Path(typath) = tyref.elem.as_ref() {