diff --git a/bin/osv/fields.py b/bin/osv/fields.py
index 9d97304aff1..f7b0b29abd3 100644
--- a/bin/osv/fields.py
+++ b/bin/osv/fields.py
@@ -31,6 +31,7 @@
 #   required
 #   size
 #
+from collections import defaultdict
 import string
 import netsvc
 import sys
@@ -430,9 +431,9 @@ class one2many(_column):
         context.update(self._context)
         if not values:
             values = {}
-        res = {}
-        for id in ids:
-            res[id] = []
+
+        res = defaultdict(list)
+
         ids2 = obj.pool.get(self._obj).search(cr, user, self._domain + [(self._fields_id, 'in', ids)], limit=self._limit, context=context)
         for r in obj.pool.get(self._obj)._read_flat(cr, user, ids2, [self._fields_id], context=context, load='_classic_write'):
             res[r[self._fields_id]].append(r['id'])