diff --git a/library/std/src/sync/rwlock.rs b/library/std/src/sync/rwlock.rs
index d967779ce361d..4e706b270963b 100644
--- a/library/std/src/sync/rwlock.rs
+++ b/library/std/src/sync/rwlock.rs
@@ -23,7 +23,9 @@ use crate::sys_common::rwlock as sys;
 ///
 /// The priority policy of the lock is dependent on the underlying operating
 /// system's implementation, and this type does not guarantee that any
-/// particular policy will be used.
+/// particular policy will be used. In particular, a writer which is waiting to
+/// acquire the lock  in `write` might or might not block future calls to
+/// `read`.
 ///
 /// The type parameter `T` represents the data that this lock protects. It is
 /// required that `T` satisfies [`Send`] to be shared across threads and