diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
index c43d1bb7..7be6c4b9 100644
--- a/serde_derive/src/de.rs
+++ b/serde_derive/src/de.rs
@@ -2476,7 +2476,7 @@ fn deserialize_map(
 
     let collected_deny_unknown_fields = if cattrs.has_flatten() && cattrs.deny_unknown_fields() {
         Some(quote! {
-            if let _serde::export::Some(_serde::export::Some((__key, _))) = __collect.into_iter().filter(|x| x.is_some()).next() {
+            if let _serde::export::Some(_serde::export::Some((__key, _))) = __collect.into_iter().filter(Option::is_some).next() {
                 if let _serde::export::Some(__key) = __key.as_str() {
                     return _serde::export::Err(
                         _serde::de::Error::custom(format_args!("unknown field `{}`", &__key)));