diff --git a/Doc/c-api/type.rst b/Doc/c-api/type.rst
index 4ba3f7ac2fafa4..be87b689fa1c22 100644
--- a/Doc/c-api/type.rst
+++ b/Doc/c-api/type.rst
@@ -82,6 +82,9 @@ Type Objects
    error (e.g. no more watcher IDs available), return ``-1`` and set an
    exception.
 
+   In free-threaded builds, :c:func:`PyType_AddWatcher` is not thread-safe,
+   so it must be called at start up (before spawning the first thread).
+
    .. versionadded:: 3.12