diff --git a/library/std/src/sync/mutex.rs b/library/std/src/sync/mutex.rs
index 3d8281fe593..d976725c276 100644
--- a/library/std/src/sync/mutex.rs
+++ b/library/std/src/sync/mutex.rs
@@ -193,6 +193,7 @@ unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
                       and cause Futures to not implement `Send`"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[clippy::has_significant_drop]
+#[cfg_attr(not(test), rustc_diagnostic_item = "MutexGuard")]
 pub struct MutexGuard<'a, T: ?Sized + 'a> {
     lock: &'a Mutex<T>,
     poison: poison::Guard,
diff --git a/library/std/src/sync/rwlock.rs b/library/std/src/sync/rwlock.rs
index 4f1b4bedaab..e956f00a12f 100644
--- a/library/std/src/sync/rwlock.rs
+++ b/library/std/src/sync/rwlock.rs
@@ -100,6 +100,7 @@ unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}
                       and cause Futures to not implement `Send`"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[clippy::has_significant_drop]
+#[cfg_attr(not(test), rustc_diagnostic_item = "RwLockReadGuard")]
 pub struct RwLockReadGuard<'a, T: ?Sized + 'a> {
     lock: &'a RwLock<T>,
 }
@@ -124,6 +125,7 @@ unsafe impl<T: ?Sized + Sync> Sync for RwLockReadGuard<'_, T> {}
                       and cause Future's to not implement `Send`"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[clippy::has_significant_drop]
+#[cfg_attr(not(test), rustc_diagnostic_item = "RwLockWriteGuard")]
 pub struct RwLockWriteGuard<'a, T: ?Sized + 'a> {
     lock: &'a RwLock<T>,
     poison: poison::Guard,
diff --git a/src/test/ui/lint/let_underscore/let_underscore_lock.stderr b/src/test/ui/lint/let_underscore/let_underscore_lock.stderr
index b7e14e8c7b5..7ff42cb1524 100644
--- a/src/test/ui/lint/let_underscore/let_underscore_lock.stderr
+++ b/src/test/ui/lint/let_underscore/let_underscore_lock.stderr
@@ -1,5 +1,5 @@
 error: non-binding let on a synchronization lock
-  --> $DIR/let_underscore_lock.rs:5:5
+  --> $DIR/let_underscore_lock.rs:6:5
    |
 LL |     let _ = data.lock().unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^