diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index b56070b0fb9..fa8de0161e6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1696,6 +1696,15 @@ include 'filename'
         turning off <varname>fsync</varname>.
        </para>
 
+       <para>
+        For reliable recovery when changing a cluster from
+        <varname>fsync</varname> off to on, it is necessary to force all
+        modified buffers in the kernel to durable storage.  This can be
+        done while the cluster is shutdown or while fsync is on by running
+        <command>initdb --sync-only</command>, running <command>sync</>,
+        unmounting the file system, or rebooting the server.
+       </para>
+
        <para>
         In many situations, turning off <xref linkend="guc-synchronous-commit">
         for noncritical transactions can provide much of the potential