diff --git a/src/Worker/DBClean.php b/src/Worker/DBClean.php
index e1777f528..eeddea4c3 100644
--- a/src/Worker/DBClean.php
+++ b/src/Worker/DBClean.php
@@ -323,7 +323,7 @@ class DBClean {
 			Config::set('system', 'dbclean-last-id-9', $last_id);
 		} elseif ($stage == 10) {
 			$last_id = Config::get('system', 'dbclean-last-id-10', 0);
-			$days = Config::get('system', 'dbclean_expire_conversation', 7);
+			$days = intval(Config::get('system', 'dbclean_expire_conversation', 7));
 
 			logger("Deleting old conversations. Last created: ".$last_id);
 			$r = dba::p("SELECT `received`, `item-uri` FROM `conversation`