diff --git a/src/Eloquent/Collection.php b/src/Eloquent/Collection.php
index 41dbebe..c31a359 100644
--- a/src/Eloquent/Collection.php
+++ b/src/Eloquent/Collection.php
@@ -3,6 +3,7 @@
 namespace Staudenmeir\LaravelAdjacencyList\Eloquent;
 
 use Illuminate\Database\Eloquent\Collection as Base;
+use RuntimeException;
 
 /**
  * @template TKey of array-key