2 files changed, 3 insertions, 1 deletions
diff --git a/library/std/src/lazy.rs b/library/std/src/lazy.rs
index 132733a0525..5afdb799f0c 100644
--- a/library/std/src/lazy.rs
+++ b/library/std/src/lazy.rs
@@ -86,7 +86,8 @@ impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SyncOnceCell<T> {}
 impl<T: UnwindSafe> UnwindSafe for SyncOnceCell<T> {}
 
 #[unstable(feature = "once_cell", issue = "74465")]
-impl<T> Default for SyncOnceCell<T> {
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T> const Default for SyncOnceCell<T> {
     /// Creates a new empty cell.
     ///
     /// # Example
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 43db3f91022..5e91a0cdbd6 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -255,6 +255,7 @@
 #![feature(const_ipv6)]
 #![feature(const_raw_ptr_deref)]
 #![feature(const_socketaddr)]
+#![feature(const_trait_impl)]
 #![feature(container_error_extra)]
 #![feature(core_intrinsics)]
 #![feature(custom_test_frameworks)]