diff --git a/liberapay/payin/common.py b/liberapay/payin/common.py
index 1eb35d88d..f727f26ac 100644
--- a/liberapay/payin/common.py
+++ b/liberapay/payin/common.py
@@ -558,6 +558,9 @@ def resolve_amounts(
 
     Returns a copy of `base_amounts` with updated values.
     """
+    if available_amount < (minimum_amount or 0):
+        raise ValueError("available_amount can't be less than minimum_amount or 0")
+
     currency = available_amount.currency
     zero = Money.ZEROS[currency]
     inf = Money('inf', currency)
diff --git a/www/%username/giving/pay/stripe/%payin_id.spt b/www/%username/giving/pay/stripe/%payin_id.spt
index 9ed8d036c..59097965c 100644
--- a/www/%username/giving/pay/stripe/%payin_id.spt
+++ b/www/%username/giving/pay/stripe/%payin_id.spt
@@ -256,7 +256,7 @@ if tippees:
     if len(tips) == 1:
         proto_transfers = resolve_tip(
             website.db, tips[0], tips[0].tippee_p, 'stripe', payer, payer.guessed_country,
-            tips[0].periodic_amount
+            tips[0].amount * 52
         )
         if len(proto_transfers) == 1:
             if proto_transfers[0].destination.country not in constants.SEPA: