diff --git a/src/wp-includes/query.php b/src/wp-includes/query.php
index b0fd38d1a1..a9300329d1 100644
--- a/src/wp-includes/query.php
+++ b/src/wp-includes/query.php
@@ -2629,7 +2629,7 @@ class WP_Query {
 		// Order search results by relevance only when another "orderby" is not specified in the query.
 		if ( ! empty( $q['s'] ) ) {
 			$search_orderby = '';
-			if ( ! empty( $q['search_orderby_title'] ) && ( empty( $q['orderby'] ) && ! $this->is_feed ) || 'relevance' === $q['orderby'] )
+			if ( ! empty( $q['search_orderby_title'] ) && ( empty( $q['orderby'] ) && ! $this->is_feed ) || ( isset( $q['orderby'] ) && 'relevance' === $q['orderby'] ) )
 				$search_orderby = $this->parse_search_order( $q );
 
 			/**