diff --git a/src/ReadOnlyCollection.php b/src/ReadOnlyCollection.php
index b9963a2..d0c1fd8 100644
--- a/src/ReadOnlyCollection.php
+++ b/src/ReadOnlyCollection.php
@@ -13,6 +13,9 @@ class ReadOnlyCollection implements CollectionInterface, IteratorAggregate {
   use ReadableCollectionTrait;
   use IterableCollectionTrait;
   
+  protected $collection = [];
+  protected $lazy = [];
+  
   public function __construct(array $initial = []) {
     $this->collection = $initial;
   }