diff --git a/bin/osv/fields.py b/bin/osv/fields.py
index f4442761bb8..fddb9742fe1 100644
--- a/bin/osv/fields.py
+++ b/bin/osv/fields.py
@@ -457,7 +457,8 @@ class one2many(_column):
 
         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'])
+            if r[self._fields_id] in res:
+                res[r[self._fields_id]].append(r['id'])
         return res
 
     def set(self, cr, obj, id, field, values, user=None, context=None):