diff --git a/phpBB/includes/functions_messenger.php b/phpBB/includes/functions_messenger.php
index 6549693333..e837811c86 100644
--- a/phpBB/includes/functions_messenger.php
+++ b/phpBB/includes/functions_messenger.php
@@ -715,14 +715,21 @@ class queue
 
 		$lock_fp = $this->lock();
 
-		set_config('last_queue_run', time(), true);
-
-		if (!file_exists($this->cache_file) || filemtime($this->cache_file) > time() - $config['queue_interval'])
+		// avoid races, check file existence once
+		$have_cache_file = file_exists($this->cache_file);
+		if (!$have_cache_file || $config['last_queue_run'] > time() - $config['queue_interval'])
 		{
+			if (!$have_cache_file)
+			{
+				set_config('last_queue_run', time(), true);
+			}
+
 			$this->unlock($lock_fp);
 			return;
 		}
 
+		set_config('last_queue_run', time(), true);
+
 		include($this->cache_file);
 
 		foreach ($this->queue_data as $object => $data_ary)