diff --git a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp
index f5be69b3d0a8..912b647d3d2c 100644
--- a/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp
+++ b/libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.mutex.requirements.mutex/thread.mutex.class/lock.pass.cpp
@@ -8,6 +8,8 @@
 //
 // UNSUPPORTED: libcpp-has-no-threads
 
+// FLAKY_TEST.
+
 // <mutex>
 
 // class mutex;