diff --git a/library/core/src/option.rs b/library/core/src/option.rs
index 8fd3bfe77b8..4e8a74d9162 100644
--- a/library/core/src/option.rs
+++ b/library/core/src/option.rs
@@ -568,6 +568,8 @@ pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E> {
 
     /// Inserts `value` into the option then returns a mutable reference to it.
     ///
+    /// If the option already contains a value, the old value is dropped.
+    ///
     /// # Example
     ///
     /// ```