diff --git a/src/TypedCollection.php b/src/TypedCollection.php
index 9871ae2..62a2987 100644
--- a/src/TypedCollection.php
+++ b/src/TypedCollection.php
@@ -4,12 +4,13 @@
 use ArrayIterator;
 use InvalidArgumentException;
 use IteratorAggregate;
+use Countable;
 
 /**
  * Class TypedCollection
  * @package GrShareCode
  */
-class TypedCollection implements IteratorAggregate
+class TypedCollection implements IteratorAggregate, Countable
 {
     /** @var array */
     private $items = [];