diff --git a/docs/library/sys.rst b/docs/library/sys.rst
index fa88a0401be3f81cfdf5f31f6e597c2c54abc251..5f5f18b463f09198e73f26868b67086333cd0c33 100644
--- a/docs/library/sys.rst
+++ b/docs/library/sys.rst
@@ -18,6 +18,7 @@ Functions
    ``sys.stdout`` by default).
 
    .. admonition:: Difference to CPython
+      :class: attention
 
       This function appears in the ``traceback`` module in CPython.