diff --git a/mps/design/prmc.txt b/mps/design/prmc.txt
index 46d55f5609e..0b1a966a50a 100644
--- a/mps/design/prmc.txt
+++ b/mps/design/prmc.txt
@@ -9,6 +9,7 @@ Protection mutator context
 :Status: complete design
 :Revision: $Id: //info.ravenbrook.com/project/mps/master/design/tests.txt#2 $
 :Copyright: See `Copyright and License`_.
+:Index terms: pair: protection mutator context; design
 
 
 Introduction