diff --git a/src/_zkapauthorizer/controller.py b/src/_zkapauthorizer/controller.py
index 5539cea4e03f306f07a388a57a57a07315d05e85..d9aab5269645bd38ad292e88edcca75e78db97c3 100644
--- a/src/_zkapauthorizer/controller.py
+++ b/src/_zkapauthorizer/controller.py
@@ -595,13 +595,13 @@ class PaymentController(object):
         for voucher in vouchers:
             if voucher.state.should_start_redemption():
                 self._log.info(
-                    "Controller found voucher ({}) at startup that needs redemption.",
+                    "Controller found voucher ({voucher}) at startup that needs redemption.",
                     voucher=voucher.number,
                 )
                 self.redeem(voucher.number)
             else:
                 self._log.info(
-                    "Controller found voucher ({}) at startup that does not need redemption.",
+                    "Controller found voucher ({voucher}) at startup that does not need redemption.",
                     voucher=voucher.number,
                 )