diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 96ea84b11f2..e341f165efd 100644
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -1112,8 +1112,10 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu
        field as compared to
        <xref linkend="guc-autovacuum-multixact-freeze-max-age"/>.  Furthermore,
        this component increases greatly once the age surpasses
-       <xref linkend="guc-vacuum-multixact-failsafe-age"/>.  The final value
-       for this component can be adjusted via
+       <xref linkend="guc-vacuum-multixact-failsafe-age"/> or when the number
+       of multixact member entries created exceeds approximately 2 billion
+       entries (see <xref linkend="vacuum-for-multixact-wraparound"/>).  The
+       final value for this component can be adjusted via
        <xref linkend="guc-autovacuum-multixact-freeze-score-weight"/>.  Note
        that increasing this parameter's value also lowers the age at which this
        component begins scaling aggressively, i.e., the scaling age is divided
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index a5a8db2ff88..e9aaf24c1be 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -3048,7 +3048,10 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
  * One exception to the previous paragraph is for tables nearing wraparound,
  * i.e., those that have surpassed the effective failsafe ages.  In that case,
  * the relfrozenxid/relminmxid-based score is scaled aggressively so that the
- * table has a decent chance of sorting to the front of the list.
+ * table has a decent chance of sorting to the front of the list.  Furthermore,
+ * the relminmxid-based score is scaled aggressively as
+ * effective_multixact_freeze_max_age is lowered due to high multixact member
+ * space usage.
  *
  * To adjust how strongly each component contributes to the score, the
  * following parameters can be adjusted from their default of 1.0 to anywhere
@@ -3194,13 +3197,15 @@ relation_needs_vacanalyze(Oid relid,
 
 	/*
 	 * To calculate the (M)XID age portion of the score, divide the age by its
-	 * respective *_freeze_max_age parameter.
+	 * respective *_freeze_max_age parameter.  The multixact_freeze_max_age
+	 * variable might be 0 here (i.e., a division-by-zero hazard), so in that
+	 * case we use the mxid_age as the MXID score.
 	 */
 	xid_age = TransactionIdIsNormal(relfrozenxid) ? recentXid - relfrozenxid : 0;
 	mxid_age = MultiXactIdIsValid(relminmxid) ? recentMulti - relminmxid : 0;
 
 	scores->xid = (double) xid_age / freeze_max_age;
-	scores->mxid = (double) mxid_age / multixact_freeze_max_age;
+	scores->mxid = (double) mxid_age / Max(1, multixact_freeze_max_age);
 
 	/*
 	 * To ensure tables are given increased priority once they begin