diff --git a/src/Jenssegers/Mongodb/Relations/EmbedsMany.php b/src/Jenssegers/Mongodb/Relations/EmbedsMany.php
index 825b0d594..85574eeb0 100644
--- a/src/Jenssegers/Mongodb/Relations/EmbedsMany.php
+++ b/src/Jenssegers/Mongodb/Relations/EmbedsMany.php
@@ -237,7 +237,7 @@ public function attach(Model $model)
     protected function associateNew($model)
     {
         // Create a new key if needed.
-        if (!$model->getAttribute('_id')) {
+        if ($model->getKeyName() === '_id' && !$model->getAttribute('_id')) {
             $model->setAttribute('_id', new ObjectID);
         }