3 files changed, 5 insertions, 2 deletions
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index d2ececaa975..1a387f291cc 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -95,6 +95,7 @@
 #![feature(const_fn_trait_bound)]
 #![feature(cow_is_borrowed)]
 #![feature(const_cow_is_borrowed)]
+#![feature(const_trait_impl)]
 #![feature(destructuring_assignment)]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 9aefd882af4..6568d9f9907 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -2105,7 +2105,8 @@ impl_eq! { Cow<'a, str>, &'b str }
 impl_eq! { Cow<'a, str>, String }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl Default for String {
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl const Default for String {
     /// Creates an empty `String`.
     #[inline]
     fn default() -> String {
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 933361d812c..87a0d371815 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -2758,7 +2758,8 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Default for Vec<T> {
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T> const Default for Vec<T> {
     /// Creates an empty `Vec<T>`.
     fn default() -> Vec<T> {
         Vec::new()