diff --git a/file/lib/data/chat/message/ChatMessageEditor.class.php b/file/lib/data/chat/message/ChatMessageEditor.class.php
index 8d5f1a1..53c10fd 100644
--- a/file/lib/data/chat/message/ChatMessageEditor.class.php
+++ b/file/lib/data/chat/message/ChatMessageEditor.class.php
@@ -24,11 +24,10 @@ class ChatMessageEditor extends \wcf\data\DatabaseObjectEditor {
 	 * @return	integer			Number of deleted messages.
 	 */
 	public static function prune($lifetime = CHAT_LOG_ARCHIVETIME) {
-		$baseClass = self::$baseClass;
 		$sql = "SELECT
-				".$baseClass::getDatabaseTableIndexName()."
+				".static::getDatabaseTableIndexName()."
 			FROM
-				".$baseClass::getDatabaseTableName()."
+				".static::getDatabaseTableName()."
 			WHERE
 				time < ?";
 		$stmt = \wcf\system\WCF::getDB()->prepareStatement($sql);
diff --git a/file/lib/data/chat/room/ChatRoomEditor.class.php b/file/lib/data/chat/room/ChatRoomEditor.class.php
index 5cc9146..8a1498a 100644
--- a/file/lib/data/chat/room/ChatRoomEditor.class.php
+++ b/file/lib/data/chat/room/ChatRoomEditor.class.php
@@ -41,21 +41,22 @@ public static function deleteAll(array $objectIDs = array()) {
 	 * @return	integer		Number of deleted rooms
 	 */
 	public static function prune() {
-		$baseClass = self::$baseClass;
 		$sql = "SELECT
-				".$baseClass::getDatabaseTableIndexName()."
+				".static::getDatabaseTableIndexName()."
 			FROM
-				".$baseClass::getDatabaseTableName()."
+				".static::getDatabaseTableName()."
 			WHERE
-				permanent = ?
-				AND roomID NOT IN(
+					permanent = ?
+				AND 	roomID NOT IN (
 					SELECT
 						fieldValue AS roomID 
 					FROM
 						wcf".WCF_N."_user_storage
 					WHERE
 							packageID = ?
-						AND	field = ?)";
+						AND	field = ?
+						AND 	fieldValue IS NOT NULL
+				)";
 		$stmt = \wcf\system\WCF::getDB()->prepareStatement($sql);
 		$stmt->execute(array(0, \wcf\util\ChatUtil::getPackageID(), 'roomID'));
 		$objectIDs = array();