diff --git a/src/Parsoid/RefGroup.php b/src/Parsoid/RefGroup.php
index 4f5ecd184..8a6b80897 100644
--- a/src/Parsoid/RefGroup.php
+++ b/src/Parsoid/RefGroup.php
@@ -23,20 +23,18 @@ class RefGroup {
 	/**
 	 * @var stdClass[]
 	 */
-	public $refs;
+	public array $refs = [];
 
 	/**
 	 * @var stdClass[]
 	 */
-	public $indexByName;
+	public array $indexByName = [];
 
 	/**
 	 * @param string $group
 	 */
 	public function __construct( string $group = '' ) {
 		$this->name = $group;
-		$this->refs = [];
-		$this->indexByName = [];
 	}
 
 	/**