diff --git a/src/Tree/Hydrator/ORM/TreeObjectHydrator.php b/src/Tree/Hydrator/ORM/TreeObjectHydrator.php
index cb1677841..4503b9725 100644
--- a/src/Tree/Hydrator/ORM/TreeObjectHydrator.php
+++ b/src/Tree/Hydrator/ORM/TreeObjectHydrator.php
@@ -249,7 +249,7 @@ protected function getChildrenField($entityClass)
             $associationMapping = $meta->getAssociationMapping($property->getName());
 
             // Make sure the association is mapped by the parent property
-            if ($associationMapping['mappedBy'] !== $this->parentField) {
+            if (!isset($associationMapping['mappedBy']) || $associationMapping['mappedBy'] !== $this->parentField) {
                 continue;
             }