diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 2b41af48a7..3537dfaade 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -823,6 +823,12 @@ Indexes:
    to remove an index.
   </para>
 
+  <para>
+   Like any long-running transaction, <command>CREATE INDEX</command> on a
+   table can affect which tuples can be removed by concurrent
+   <command>VACUUM</command> on any other table.
+  </para>
+
   <para>
    Prior releases of <productname>PostgreSQL</productname> also had an
    R-tree index method.  This method has been removed because
diff --git a/doc/src/sgml/ref/reindex.sgml b/doc/src/sgml/ref/reindex.sgml
index df1759b0f1..ef0e576d1e 100644
--- a/doc/src/sgml/ref/reindex.sgml
+++ b/doc/src/sgml/ref/reindex.sgml
@@ -404,6 +404,12 @@ Indexes:
     CONCURRENTLY</command> cannot.
    </para>
 
+   <para>
+    Like any long-running transaction, <command>REINDEX</command> on a table
+    can affect which tuples can be removed by concurrent
+    <command>VACUUM</command> on any other table.
+   </para>
+
    <para>
     <command>REINDEX SYSTEM</command> does not support
     <command>CONCURRENTLY</command> since system catalogs cannot be reindexed