diff --git a/zerocopy-derive/src/lib.rs b/zerocopy-derive/src/lib.rs
index b3d99dac75..8e1b980199 100644
--- a/zerocopy-derive/src/lib.rs
+++ b/zerocopy-derive/src/lib.rs
@@ -661,7 +661,7 @@ fn impl_block<D: DataExt>(
     let use_concrete = if input.generics.params.is_empty() {
         Some(quote! {
             const _: () = {
-                fn must_implement_trait<T: zerocopy::#trait_ident + ?Sized>() {}
+                fn must_implement_trait<T: zerocopy::#trait_ident + ?::core::marker::Sized>() {}
                 let _ = must_implement_trait::<#type_ident>;
             };
         })