diff --git a/lib/Relation/HasMany.php b/lib/Relation/HasMany.php
index 7643b8a..0366b15 100644
--- a/lib/Relation/HasMany.php
+++ b/lib/Relation/HasMany.php
@@ -114,7 +114,7 @@ public function save(EntityInterface $entity, $relationName, $options = [])
             }
 
             foreach ($oldEntities as $oldRelatedEntity) {
-                if (!in_array($oldRelatedEntity, $relatedIds)) {
+                if (!in_array($oldRelatedEntity->primaryKey(), $relatedIds)) {
                     $deletedIds[] = $oldRelatedEntity->primaryKey();
                 }
             }