diff --git a/Documentation/config-mail.txt b/Documentation/config-mail.txt
index 686dfb8..40a6284 100644
--- a/Documentation/config-mail.txt
+++ b/Documentation/config-mail.txt
@@ -229,6 +229,10 @@
 +
 The Gerrit instance name, followed by the short project name
 
+$addInstanceNameInSubject::
++
+Whether the instance name should be included in the email subject.
+
 $sshHost::
 +
 SSH hostname for the Gerrit instance.