diff --git a/src/test/modules/test_autovacuum/t/001_parallel_autovacuum.pl b/src/test/modules/test_autovacuum/t/001_parallel_autovacuum.pl
--- a/src/test/modules/test_autovacuum/t/001_parallel_autovacuum.pl
+++ b/src/test/modules/test_autovacuum/t/001_parallel_autovacuum.pl
@@ -8,6 +8,7 @@
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 use Test::More;
+use Time::HiRes qw(usleep);
 
 if ($ENV{enable_injection_points} ne 'yes')
 {
@@ -395,5 +396,78 @@
 $node->safe_psql('postgres',
 	"SELECT injection_points_detach('autovacuum-worker-cost-balanced')");
 
+
+# Test 6 (added for review):
+# The reverse of test 5: a worker LEAVES the balance while the leader waits.
+# That rebalance takes another path: the leaving worker sets AutoVacRebalance
+# in FreeWorkerInfo(), and the launcher recalculates the count.
+
+$node->poll_query_until(
+	'postgres', q{
+	SELECT count(*) = 0 FROM pg_stat_activity
+	WHERE backend_type = 'autovacuum worker' AND datname = 'regress_db2'
+}) or die "second autovacuum worker from test 5 did not finish";
+
+prepare_for_next_test($node, 6);
+$node->safe_psql('regress_db2',
+	'ALTER TABLE filler SET (autovacuum_enabled = false)');
+$node->safe_psql('regress_db2', 'UPDATE filler SET id = id + 1 WHERE true');
+$log_offset = -s $node->logfile;
+
+start_leader_waiting_for_worker($node);
+
+# A second worker joins and is held, as in test 5: the leader goes to 400.
+$node->safe_psql('postgres',
+	"SELECT injection_points_attach('autovacuum-worker-cost-balanced', 'wait')"
+);
+$node->safe_psql('regress_db2',
+	'ALTER TABLE filler SET (autovacuum_enabled = true)');
+$node->wait_for_log(
+	qr/Autovacuum VacuumUpdateCosts\(db=$postgresoid, rel=$testautovacoid, dobalance=yes, cost_limit=400,/,
+	$log_offset);
+
+# Now let the second worker finish and leave, with the leader still waiting.
+my $leave_offset = -s $node->logfile;
+$node->safe_psql('postgres',
+	"SELECT injection_points_wakeup('autovacuum-worker-cost-balanced')");
+$node->safe_psql('postgres',
+	"SELECT injection_points_detach('autovacuum-worker-cost-balanced')");
+$node->poll_query_until(
+	'postgres', q{
+	SELECT count(*) = 0 FROM pg_stat_activity
+	WHERE backend_type = 'autovacuum worker' AND datname = 'regress_db2'
+}) or die "second autovacuum worker did not finish";
+my $left_at = time;
+
+# The waiting leader should go back to the whole limit.  Poll the log for up
+# to 30 s instead of the default timeout.
+my $seen = 0;
+for (my $i = 0; $i < 300; $i++)
+{
+	if (slurp_file($node->logfile, $leave_offset) =~
+		/Autovacuum VacuumUpdateCosts\(db=$postgresoid, rel=$testautovacoid, dobalance=yes, cost_limit=800,/)
+	{
+		$seen = 1;
+		last;
+	}
+	usleep(100_000);
+}
+my $still_waiting = $node->safe_psql(
+	'postgres', q{
+	SELECT count(*) FROM pg_stat_activity
+	WHERE backend_type = 'autovacuum worker' AND wait_event = 'ParallelFinish'});
+note("leader still in ParallelFinish when checked: $still_waiting; waited "
+	  . (time - $left_at) . " s");
+ok($seen, 'waiting leader returns to the whole limit when a worker leaves');
+
+release_worker($node);
+$node->wait_for_log(
+	qr/automatic vacuum of table "postgres\.public\.test_autovac"/,
+	$leave_offset);
+my @limits6 =
+  slurp_file($node->logfile, $leave_offset) =~
+  /parallel autovacuum worker updated cost params: cost_limit=(\d+),/g;
+note("parallel worker cost_limit sequence after the worker left: @limits6");
+is($limits6[-1] // 'none', '800', 'parallel worker ends at the whole limit');
 $node->stop;
 done_testing();