diff --git a/PropertyDescriber/ObjectPropertyDescriber.php b/PropertyDescriber/ObjectPropertyDescriber.php
index ef1aabc..d5836c0 100644
--- a/PropertyDescriber/ObjectPropertyDescriber.php
+++ b/PropertyDescriber/ObjectPropertyDescriber.php
@@ -28,7 +28,10 @@ class ObjectPropertyDescriber implements PropertyDescriberInterface, ModelRegist
             false,
             $types[0]->getClassName(),
             $types[0]->isCollection(),
-            $types[0]->getCollectionKeyType(),
+            // BC layer for symfony < 5.3
+            method_exists($types[0], 'getCollectionKeyTypes') ?
+                ($types[0]->getCollectionKeyTypes()[0] ?? null) :
+                $types[0]->getCollectionKeyType(),
             // BC layer for symfony < 5.3
             method_exists($types[0], 'getCollectionValueTypes') ?
                 ($types[0]->getCollectionValueTypes()[0] ?? null) :