diff --git a/library/alloc/src/boxed/thin.rs b/library/alloc/src/boxed/thin.rs
index f83c8f83cc98..a8005b7067d0 100644
--- a/library/alloc/src/boxed/thin.rs
+++ b/library/alloc/src/boxed/thin.rs
@@ -171,6 +171,7 @@ fn with_header(&self) -> &WithHeader<<T as Pointee>::Metadata> {
 /// An opaque representation of `WithHeader<H>` to avoid the
 /// projection invariance of `<T as Pointee>::Metadata`.
 #[repr(transparent)]
+#[allow(unused_tuple_struct_fields)] // Field only used through `WithHeader` type above.
 struct WithOpaqueHeader(NonNull<u8>);
 
 impl WithOpaqueHeader {