diff --git a/src/Types/AbstractList.php b/src/Types/AbstractList.php
index ee8ace8..d5fe03d 100644
--- a/src/Types/AbstractList.php
+++ b/src/Types/AbstractList.php
@@ -45,6 +45,11 @@ public function __construct(?Type $valueType = null, ?Type $keyType = null)
         $this->keyType        = $keyType;
     }
 
+    public function getOriginalKeyType(): ?Type
+    {
+        return $this->keyType;
+    }
+
     /**
      * Returns the type for the keys of this array.
      */