diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 385ee20d0cf..59d521b23b6 100644
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -356,7 +356,7 @@
     <productname>PostgreSQL</productname> distinguishes a special XID
     <literal>FrozenXID</>.  This XID is always considered older
     than every normal XID. Normal XIDs are
-    compared using modulo-2<superscript>31</> arithmetic. This means
+    compared using modulo-2<superscript>32</> arithmetic. This means
     that for every normal XID, there are two billion XIDs that are
     <quote>older</> and two billion that are <quote>newer</>; another
     way to say it is that the normal XID space is circular with no
diff --git a/src/backend/access/transam/transam.c b/src/backend/access/transam/transam.c
index aa0881ae00a..43f7c54d1d9 100644
--- a/src/backend/access/transam/transam.c
+++ b/src/backend/access/transam/transam.c
@@ -305,7 +305,7 @@ TransactionIdPrecedes(TransactionId id1, TransactionId id2)
 {
 	/*
 	 * If either ID is a permanent XID then we can just do unsigned
-	 * comparison.	If both are normal, do a modulo-2^31 comparison.
+	 * comparison.	If both are normal, do a modulo-2^32 comparison.
 	 */
 	int32		diff;