diff --git a/account_financial_report_webkit/report/aged_partner_balance.py b/account_financial_report_webkit/report/aged_partner_balance.py
index 5566ee49..7fc1b904 100644
--- a/account_financial_report_webkit/report/aged_partner_balance.py
+++ b/account_financial_report_webkit/report/aged_partner_balance.py
@@ -191,7 +191,7 @@ class AccountAgedTrialBalanceWebkit(PartnersOpenInvoicesWebkit):
             reference_line = sale_lines[0]
         elif len(refund_lines) == 1:
             reference_line = refund_lines[0]
-        key = line.get('date_maturity', 'ldate')
+        key = 'date_maturity' if line.get('date_maturity') else 'ldate'
         return self._compute_delay_from_key(key,
                                             reference_line,
                                             end_date)