diff --git a/impl/src/bitfield.rs b/impl/src/bitfield.rs
index bbcbff3..f0cd2ed 100644
--- a/impl/src/bitfield.rs
+++ b/impl/src/bitfield.rs
@@ -68,12 +68,12 @@ impl TryFrom<(&mut Config, syn::ItemStruct)> for BitfieldStruct {
     type Error = syn::Error;
 
     fn try_from(
-        (config, mut item_struct): (&mut Config, syn::ItemStruct),
+        (config, item_struct): (&mut Config, syn::ItemStruct),
     ) -> Result<Self> {
         Self::ensure_has_fields(&item_struct)?;
         Self::ensure_no_generics(&item_struct)?;
         Self::ensure_no_bits_markers(&item_struct)?;
-        Self::extract_repr(&mut item_struct.attrs, config)?;
+        Self::extract_repr(&item_struct.attrs, config)?;
         Ok(Self { item_struct })
     }
 }