diff --git a/kingfisher_scrapy/log_formatter.py b/kingfisher_scrapy/log_formatter.py
index 995d17ce..9b60e8b7 100644
--- a/kingfisher_scrapy/log_formatter.py
+++ b/kingfisher_scrapy/log_formatter.py
@@ -15,6 +15,6 @@ def _omit_data(self, method, item, *args):
         """
         Omits an item's `data` value from the log message.
         """
-        item = item.copy()
+        item = item.__dict__.copy()
         item.pop('data', None)
         return getattr(super(), method)(item, *args)