diff --git a/docs/contracts/using-for.rst b/docs/contracts/using-for.rst
index c8414de9d..7da1ffd23 100644
--- a/docs/contracts/using-for.rst
+++ b/docs/contracts/using-for.rst
@@ -1,4 +1,4 @@
-.. index:: ! using for, library
+.. index:: ! using for, library, ! operator; user-defined
 
 .. _using-for: