diff --git a/library/includes/cron/jobs/clean_pm.php b/library/includes/cron/jobs/clean_pm.php
index 754f0d4a..45e9cc14 100644
--- a/library/includes/cron/jobs/clean_pm.php
+++ b/library/includes/cron/jobs/clean_pm.php
@@ -6,8 +6,29 @@ $pm_days_keep = (int) $bb_cfg['pm_days_keep'];
 
 if ($pm_days_keep != 0)
 {
-	DB()->query("
-		DELETE FROM ". BB_PRIVMSGS ."
-		WHERE privmsgs_date < ". (TIMENOW - 86400*$pm_days_keep) ."
-	");
+	$per_cycle = 20000;
+	$row = DB()->fetch_row("SELECT MIN(privmsgs_id) AS start_id, MAX(privmsgs_id) AS finish_id FROM " . BB_PRIVMSGS);
+	$start_id = (int) $row['start_id'];
+	$finish_id = (int) $row['finish_id'];
+
+	while (true)
+	{
+		set_time_limit(600);
+		$end_id = $start_id + $per_cycle - 1;
+
+		DB()->query("
+			DELETE FROM " . BB_PRIVMSGS . "
+			WHERE privmsgs_id BETWEEN $start_id AND $end_id
+				AND privmsgs_date < " . (TIMENOW - 86400 * $pm_days_keep) . "
+		");
+		if ($end_id > $finish_id)
+		{
+			break;
+		}
+		if (!($start_id % ($per_cycle * 10)))
+		{
+			sleep(1);
+		}
+		$start_id += $per_cycle;
+	}
 }