diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 211ad03d954..e34426ff18f 100644
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -658,11 +658,12 @@ HINT:  Stop the postmaster and vacuum that database in single-user mode.
     <para>
      As a safety device, a whole-table vacuum scan will occur for any table
      whose multixact-age is greater than
-     <xref linkend="guc-autovacuum-multixact-freeze-max-age">.
-     This will occur even if autovacuum is nominally disabled.  Whole-table
+     <xref linkend="guc-autovacuum-multixact-freeze-max-age">.  Whole-table
      vacuum scans will also occur progressively for all tables, starting with
      those that have the oldest multixact-age, if the amount of used member
-     storage space exceeds the amount 25% of the addressible storage space.
+     storage space exceeds the amount 50% of the addressible storage space.
+     Both of these kinds of whole-table scans will occur even if autovacuum is
+     nominally disabled.
     </para>
    </sect3>
   </sect2>
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index fc0e4e74004..d92cbccaf8a 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -169,7 +169,7 @@
 	 ((xid) % MULTIXACT_MEMBERS_PER_MEMBERGROUP) * sizeof(TransactionId))
 
 /* Multixact members wraparound thresholds. */
-#define MULTIXACT_MEMBER_SAFE_THRESHOLD		(MaxMultiXactOffset / 4)
+#define MULTIXACT_MEMBER_SAFE_THRESHOLD		(MaxMultiXactOffset / 2)
 #define MULTIXACT_MEMBER_DANGER_THRESHOLD	\
 	(MaxMultiXactOffset - MaxMultiXactOffset / 4)