diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index a3209d0..cce2858 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -1554,6 +1573,9 @@ pg_notification_queue_usage(PG_FUNCTION_ARGS)
 {
 	double		usage;
 
+	/* Advance the queue tail so we don't report a too-large result */
+	asyncQueueAdvanceTail();
+
 	LWLockAcquire(AsyncQueueLock, LW_SHARED);
 	usage = asyncQueueUsage();
 	LWLockRelease(AsyncQueueLock);