diff --git a/src/liballoc/collections/binary_heap.rs b/src/liballoc/collections/binary_heap.rs
index 9f531f5b83c75..3d04f30e7bde5 100644
--- a/src/liballoc/collections/binary_heap.rs
+++ b/src/liballoc/collections/binary_heap.rs
@@ -1163,6 +1163,9 @@ impl<T> FusedIterator for Drain<'_, T> {}
 
 #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
 impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
+    /// Converts a `Vec<T>` into a `BinaryHeap<T>`.
+    ///
+    /// This conversion happens in-place, and has `O(n)` time complexity.
     fn from(vec: Vec<T>) -> BinaryHeap<T> {
         let mut heap = BinaryHeap { data: vec };
         heap.rebuild();