diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 2b0e3951..9bc18e02 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -1215,6 +1215,7 @@ class FileField(BaseField):
 
             # Create a new proxy object as we don't already have one
             instance._data[key] = self.proxy_class(key=key, instance=instance,
+                                                   db_alias=self.db_alias,
                                                    collection_name=self.collection_name)
             instance._data[key].put(value)
         else: