diff --git a/chellow/e/bill_parsers/mm.py b/chellow/e/bill_parsers/mm.py
index bf8b919e3..1726c4d97 100644
--- a/chellow/e/bill_parsers/mm.py
+++ b/chellow/e/bill_parsers/mm.py
@@ -313,7 +313,7 @@ def _handle_1600(headers, pre_record, record):
     )
     late_payment_gbp = Decimal(parts["late_payment_fee"]) / Decimal(100)
 
-    headers["breakdown"]["late_payment_gbp"] += late_payment_gbp
+    headers["breakdown"]["late-payment-gbp"] += late_payment_gbp
 
 
 def _handle_1700(headers, pre_record, record):