diff --git a/addons/document/document.py b/addons/document/document.py
index df12431df7a..56324c6c462 100644
--- a/addons/document/document.py
+++ b/addons/document/document.py
@@ -110,8 +110,11 @@ class document_file(osv.osv):
             ids.extend(parents[parent_id])
 
         # sort result according to the original sort ordering
-        ids = [id for id in orig_ids if id in ids]
-        return len(ids) if count else ids
+        if count:
+            return len(ids)
+        else:
+            set_ids = set(ids)
+            return [id for id in orig_ids if id in set_ids]
 
     def copy(self, cr, uid, id, default=None, context=None):
         if not default: