diff --git a/invoice/src/main/java/org/killbill/billing/invoice/InvoicePluginDispatcher.java b/invoice/src/main/java/org/killbill/billing/invoice/InvoicePluginDispatcher.java
index ec32fd3..f75462e 100644
--- a/invoice/src/main/java/org/killbill/billing/invoice/InvoicePluginDispatcher.java
+++ b/invoice/src/main/java/org/killbill/billing/invoice/InvoicePluginDispatcher.java
@@ -214,7 +214,7 @@ public class InvoicePluginDispatcher {
mutableField("prettyUsageName", existingItem != null ? existingItem.getPrettyUsageName() : null, additionalInvoiceItem.getPrettyUsageName(), invoicePlugin),
immutableField("startDate", existingItem, existingItem != null ? existingItem.getStartDate() : null, additionalInvoiceItem.getStartDate(), invoicePlugin),
immutableField("endDate", existingItem, existingItem != null ? existingItem.getEndDate() : null, additionalInvoiceItem.getEndDate(), invoicePlugin),
- immutableField("amount", existingItem, existingItem != null ? existingItem.getAmount() : null, additionalInvoiceItem.getAmount(), invoicePlugin),
+ mutableField("amount", existingItem != null ? existingItem.getAmount() : null, additionalInvoiceItem.getAmount(), invoicePlugin),
immutableField("rate", existingItem, existingItem != null ? existingItem.getRate() : null, additionalInvoiceItem.getRate(), invoicePlugin),
immutableField("currency", existingItem, existingItem != null ? existingItem.getCurrency() : null, additionalInvoiceItem.getCurrency(), invoicePlugin),
immutableField("linkedItemId", existingItem, existingItem != null ? existingItem.getLinkedItemId() : null, additionalInvoiceItem.getLinkedItemId(), invoicePlugin),