diff --git a/trytond/model/modelstorage.py b/trytond/model/modelstorage.py
index f6a39bbf31..dfab5ccb13 100644
--- a/trytond/model/modelstorage.py
+++ b/trytond/model/modelstorage.py
@@ -566,7 +566,7 @@ class ModelStorage(Model):
                     warn('too_many_relations_found', value, relation)
                     res = None
                 else:
-                    res = res[0]
+                    res = res[0].id
                 return res
 
             def get_many2many(relation, value):
@@ -586,7 +586,7 @@ class ModelStorage(Model):
                     else:
                         res.extend(res2)
                 if len(res):
-                    res = [('set', res)]
+                    res = [('set', [x.id for x in res])]
                 return res
 
             def get_one2one(relation, value):