diff --git a/nutype_macros/src/common/gen/parse_error.rs b/nutype_macros/src/common/gen/parse_error.rs
index 2780b38..c45f361 100644
--- a/nutype_macros/src/common/gen/parse_error.rs
+++ b/nutype_macros/src/common/gen/parse_error.rs
@@ -67,36 +67,32 @@ pub fn gen_def_parse_error(
         }
     };
 
-    cfg_if! {
-        if #[cfg(ERROR_IN_CORE)] {
-            let generics_with_fromstr_and_debug_bounds = add_bound_to_all_type_params(
-                &generics_with_fromstr_bound,
-                syn::parse_quote!(::core::fmt::Debug),
-            );
-            let impl_error = quote! {
-                impl #generics_with_fromstr_and_debug_bounds ::core::error::Error for #parse_error_type_name #generics_without_bounds {
-                    fn source(&self) -> Option<&(dyn ::core::error::Error + 'static)> {
-                        None
-                    }
-                }
-            };
-        } else if #[cfg(feature = "std")] {
-            let generics_with_fromstr_and_debug_bounds = add_bound_to_all_type_params(
-                &generics_with_fromstr_bound,
-                syn::parse_quote!(::core::fmt::Debug),
-            );
-            let impl_error = quote! {
-                impl #generics_with_fromstr_and_debug_bounds ::std::error::Error for #parse_error_type_name #generics_without_bounds {
-                    fn source(&self) -> Option<&(dyn ::std::error::Error + 'static)> {
-                        None
-                    }
+    #[allow(unused_assignments, reason = "Sometimes triggered when developping nutype due to feature flags.")]
+    let mut impl_error = quote! {};
+
+    #[cfg(any(ERROR_IN_CORE, feature = "std"))]
+    {
+        let generics_with_fromstr_and_debug_bounds = add_bound_to_all_type_params(
+            &generics_with_fromstr_bound,
+            syn::parse_quote!(::core::fmt::Debug),
+        );
+
+        cfg_if! { 
+            if #[cfg(ERROR_IN_CORE)] {
+                let error = quote! { ::core::error::Error };
+            } else {
+                let error = quote! { ::std::error::Error };
+            }
+        };
+
+        impl_error = quote! {
+            impl #generics_with_fromstr_and_debug_bounds #error for #parse_error_type_name #generics_without_bounds {
+                fn source(&self) -> Option<&(dyn ::core::error::Error + 'static)> {
+                    None
                 }
-            };
-        } else {
-            // NOTE: `::core::error::Error` is stable only for rust >= 1.81.0.
-            let impl_error = quote! {};
-        }
-    };
+            }
+        };
+    }
 
     quote! {
         #definition