diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index e1806a9a28a..b51df2a4606 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -812,6 +812,17 @@ WaitForParallelWorkersToFinish(ParallelContext *pcxt)
 		 */
 		CHECK_FOR_INTERRUPTS();
 
+		/*
+		 * An autovacuum worker running a parallel vacuum (leader) propagates
+		 * changes to the cost-based delay parameters to its parallel workers
+		 * at its own cost delay points, which it no longer reaches while
+		 * waiting here. Do it here instead, on every wakeup, so that a config
+		 * reload or a change in the number of autovacuum workers sharing the
+		 * cost limit reaches the parallel workers before they finish.
+		 */
+		if (AmAutoVacuumWorkerProcess())
+			parallel_vacuum_refresh_cost_params();
+
 		for (i = 0; i < pcxt->nworkers_launched; ++i)
 		{
 			/*
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index d4572861000..da0ec3cc8ee 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -43,6 +43,7 @@
 #include "executor/instrument.h"
 #include "optimizer/paths.h"
 #include "pgstat.h"
+#include "postmaster/interrupt.h"
 #include "storage/bufmgr.h"
 #include "storage/proc.h"
 #include "tcop/tcopprot.h"
@@ -729,6 +730,40 @@ parallel_vacuum_propagate_shared_delay_params(void)
 	pg_atomic_fetch_add_u32(&pv_shared_cost_params->generation, 1);
 }
 
+/*
+ * Reload the configuration file if requested, and refresh the cost-based
+ * delay parameters of an autovacuum worker running a parallel vacuum
+ * (leader), propagating any change to its parallel workers.
+ */
+void
+parallel_vacuum_refresh_cost_params(void)
+{
+	Assert(AmAutoVacuumWorkerProcess());
+
+	/*
+	 * Quick return if the leader is not sharing the delay parameters with
+	 * parallel workers.
+	 */
+	if (pv_shared_cost_params == NULL)
+		return;
+
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+		ProcessConfigFile(PGC_SIGHUP);
+
+		/* This re-divides the cost limit too */
+		VacuumUpdateCosts();
+	}
+	else
+	{
+		/* The number of workers sharing the cost limit may have changed */
+		AutoVacuumUpdateCostLimit();
+	}
+
+	parallel_vacuum_propagate_shared_delay_params();
+}
+
 /*
  * Compute the number of parallel worker processes to request.  Both index
  * vacuum and index cleanup can be executed with parallel workers.
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 60ebe828900..0ec01c5da6f 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -1814,8 +1814,33 @@ autovac_recalculate_workers_for_balance(void)
 	}
 
 	if (nworkers_for_balance != orig_nworkers_for_balance)
+	{
 		pg_atomic_write_u32(&AutoVacuumShmem->av_nworkersForBalance,
 							nworkers_for_balance);
+
+		/*
+		 * Wake up the autovacuum workers sharing the cost limit so that they
+		 * pick up the new count. An autovacuum worker that is vacuuming does
+		 * that on its next nap anyway, but one running a parallel vacuum
+		 * (leader) that is only waiting for its parallel workers to finish
+		 * never naps, and nothing else would tell it.
+		 *
+		 * Only the waiting leaders need this, but knowing which ones are
+		 * waiting would need more state. For an autovacuum worker that is not
+		 * in a latch wait, SetLatch() sends no signal and only marks the
+		 * latch set, which costs one early return from its next latch wait.
+		 */
+		dlist_foreach(iter, &AutoVacuumShmem->av_runningWorkers)
+		{
+			WorkerInfo	worker = dlist_container(WorkerInfoData, wi_links, iter.cur);
+
+			if (worker->wi_proc == NULL ||
+				pg_atomic_unlocked_test_flag(&worker->wi_dobalance))
+				continue;
+
+			SetLatch(&worker->wi_proc->procLatch);
+		}
+	}
 }
 
 /*
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index 6e3c912bf5c..89fa1fcd261 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -432,6 +432,7 @@ extern void parallel_vacuum_cleanup_all_indexes(ParallelVacuumState *pvs,
 												PVWorkerStats *wstats);
 extern void parallel_vacuum_update_shared_delay_params(void);
 extern void parallel_vacuum_propagate_shared_delay_params(void);
+extern void parallel_vacuum_refresh_cost_params(void);
 extern void parallel_vacuum_main(dsm_segment *seg, shm_toc *toc);
 
 /* in commands/analyze.c */