diff --git a/etl/epc/Record.py b/etl/epc/Record.py
index 3f64a7c5..e654aa67 100644
--- a/etl/epc/Record.py
+++ b/etl/epc/Record.py
@@ -354,7 +354,7 @@ class EPCRecord:
                 if v != self._prepared_epc.get(k) and (not pd.isnull(v)) and (not pd.isnull(self._prepared_epc.get(k))):
                     self.landlord_differences[k] = v
 
-        self.prepared_epc.update(self.landlord_differences)
+        self._prepared_epc.update(self.landlord_differences)
 
     @staticmethod
     def _calculate_days_to(lodgement_date: Union[str, pd.Series]) -> Union[int, pd.Series]:
@@ -1056,7 +1056,7 @@ class EPCRecord:
         return difference_record
 
     def _require_prepared_epc(self) -> None:
-        if self.prepared_epc is None:
+        if self._prepared_epc is None:
             raise ValueError("EPCRecord does not contain prepared EPC data")
 
     def __sub__(self, other):