# Technical data
     code                  = CharField(_('code'), unique=True, required=True, validators=[is_valid_collection_code])
-    old_code              = CharField(_('old code'), unique=True, null=True)
+    old_code              = CharField(_('old code'), null=True)
     approx_duration       = DurationField(_('approximative duration'))
     physical_items_num    = IntegerField(_('number of components (medium / piece)'))
     physical_format       = WeakForeignKey('PhysicalFormat', related_name="collections", 
     
     # Archiving data
     code                  = CharField(_('code'), unique=True, null=True)
-    old_code              = CharField(_('old code'), unique=True, null=True)
+    old_code              = CharField(_('old code'), null=True)
     track                 = CharField(_('item number'))
     creator_reference     = CharField(_('reference'))
     external_references   = TextField(_('published reference'))