diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 5d864be510c..ef8b57e0ebe 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -1,5 +1,5 @@
@@ -227,7 +227,8 @@ where action is one of:
This form removes the most recently used
- index specification from the table.
+ index specification from the table. This affects
+ future cluster operations that don't specify an index.