diff --git a/includes/EmailBatch.php b/includes/EmailBatch.php
index a7110aedc..b72b15e76 100644
--- a/includes/EmailBatch.php
+++ b/includes/EmailBatch.php
@@ -290,7 +290,7 @@ class EmailBatch {
 		$iterator->addConditions( [ 'eeb_user_id' => $this->mUser->getId() ] );
 		if ( $this->lastEvent ) {
 			// There is a processed cutoff point
-			$iterator->addConditions( [ 'eeb_event_id <= ' . (int)$this->lastEvent ] );
+			$iterator->addConditions( [ $dbr->expr( 'eeb_event_id', '<=', (int)$this->lastEvent ) ] );
 		}
 		$iterator->setCaller( __METHOD__ );
 
diff --git a/includes/Mapper/NotificationMapper.php b/includes/Mapper/NotificationMapper.php
index 75732853b..804e3bc9a 100644
--- a/includes/Mapper/NotificationMapper.php
+++ b/includes/Mapper/NotificationMapper.php
@@ -135,7 +135,8 @@ class NotificationMapper extends AbstractMapper {
 		array $titles = null,
 		$dbSource = DB_REPLICA
 	) {
-		$conds = [ 'notification_read_timestamp IS NOT NULL' ];
+		$dbr = $this->dbFactory->getEchoDb( $dbSource );
+		$conds = [ $dbr->expr( 'notification_read_timestamp', '!=', null ) ];
 		if ( $titles ) {
 			$conds['event_page_id'] = $this->getIdsForTitles( $titles );
 			if ( !$conds['event_page_id'] ) {
@@ -366,7 +367,7 @@ class NotificationMapper extends AbstractMapper {
 		);
 		$iterator->addConditions( [
 			'notification_user' => $userId,
-			'notification_event < ' . (int)$eventId
+			$dbw->expr( 'notification_event', '<', (int)$eventId ),
 		] );
 		$iterator->setCaller( __METHOD__ );
 
diff --git a/maintenance/removeOrphanedEvents.php b/maintenance/removeOrphanedEvents.php
index 58754b070..4b97c34d7 100644
--- a/maintenance/removeOrphanedEvents.php
+++ b/maintenance/removeOrphanedEvents.php
@@ -73,7 +73,7 @@ class RemoveOrphanedEvents extends LoggedUpdateMaintenance {
 		$iterator->addConditions( [
 			'notification_user' => null,
 			'eeb_user_id' => null,
-			'event_id < ' . $maxId
+			$dbr->expr( 'event_id', '<', $maxId ),
 		] );
 		$iterator->setCaller( __METHOD__ );
 
@@ -113,7 +113,7 @@ class RemoveOrphanedEvents extends LoggedUpdateMaintenance {
 		$iterator->addConditions(
 			[
 				'event_type' => null,
-				'etp_event < ' . $maxId
+				$dbr->expr( 'etp_event', '<', $maxId ),
 			]
 		);
 		$iterator->addOptions( [ 'DISTINCT' ] );