diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index a6ca55dafe53652..1c6fd5af3933f31 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -1741,6 +1741,9 @@ returns a boolean value regardless of the type of its argument
 (for example, ``not 'foo'`` produces ``False`` rather than ``''``.)
 
 
+.. index::
+  single: := (colon equals)
+
 Assignment expressions
 ======================