diff --git a/phpBB/phpbb/search/backend/fulltext_postgres.php b/phpBB/phpbb/search/backend/fulltext_postgres.php
index 535e298e13..d9a7c366da 100644
--- a/phpBB/phpbb/search/backend/fulltext_postgres.php
+++ b/phpBB/phpbb/search/backend/fulltext_postgres.php
@@ -65,7 +65,7 @@ class fulltext_postgres extends base implements search_backend_interface
 	 * Operators are prefixed in search query and common words excluded
 	 * @var string
 	 */
-	protected $search_query;
+	protected $search_query = '';
 
 	/**
 	 * Contains common words.