diff --git a/mps/manual/source/design/index.rst b/mps/manual/source/design/index.rst
index 6a7dd9c23f7..92e59523eeb 100644
--- a/mps/manual/source/design/index.rst
+++ b/mps/manual/source/design/index.rst
@@ -3,6 +3,15 @@
 Design
 ******
 
+.. warning::
+
+    Much of the documentation in this section is very old: some of it
+    dates back to the origin of the MPS in 1995. It has not been
+    brought up to date or checked for correctness, so it is mainly of
+    historical interest. As pieces of documentation are brought up to
+    date, they will be moved to the :ref:`internals` section.
+
+
 .. toctree::
     :numbered: