diff --git a/pytools/tag.py b/pytools/tag.py
index b6b11cf26a79685f9ad01a4287783422ba9fab6d..fcf16ac767c1a0941d9485267b97f53b2572db35 100644
--- a/pytools/tag.py
+++ b/pytools/tag.py
@@ -49,6 +49,13 @@ Supporting Functionality
 .. autoclass:: DottedName
 .. autoclass:: NonUniqueTagError
 
+
+Internal stuff that is only here because the documentation tool wants it
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. class:: T_co
+
+    A covariant type variable used in, e.g. :class:`Taggable.copy`.
 """
 
 #  }}}