diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 9da230915b8..0e03551286e 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -358,7 +358,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// let mut set: BTreeSet<i32> = BTreeSet::new_in(Global);
     /// ```
     #[unstable(feature = "btreemap_alloc", issue = "32838")]
-    pub fn new_in(alloc: A) -> BTreeSet<T, A> {
+    pub const fn new_in(alloc: A) -> BTreeSet<T, A> {
         BTreeSet { map: BTreeMap::new_in(alloc) }
     }