diff --git a/conservancy_beancount/data.py b/conservancy_beancount/data.py
index 86a06c7f57c808309019c954603f8997481d7124..b6903d30ec98aae486514d2e41efd997baa5eab9 100644
--- a/conservancy_beancount/data.py
+++ b/conservancy_beancount/data.py
@@ -132,6 +132,15 @@ class Amount(bc_amount.Amount):
     """
     number: decimal.Decimal
 
+    # beancount.core._Amount is the plain namedtuple.
+    # beancore.core.Amount adds instance methods to it.
+    # b.c.Amount.__New__ calls `b.c._Amount.__new__`, which confuses type
+    # checking. See <https://github.com/python/mypy/issues/1279>.
+    # It works fine if you use super(), which is better practice anyway.
+    # So we override __new__ just to call _Amount.__new__ this way.
+    def __new__(cls, number: decimal.Decimal, currency: str) -> 'Amount':
+        return super(bc_amount._Amount, Amount).__new__(cls, number, currency)
+
 
 class Metadata(MutableMapping[MetaKey, MetaValue]):
     """Transaction or posting metadata
@@ -309,7 +318,7 @@ def balance_of(txn: Transaction,
         ]
         number = sum((wt.number for wt in weights), number)
         currency = weights[0].currency
-    return Amount._make((number, currency))
+    return Amount(number, currency)
 
 @functools.lru_cache()
 def is_opening_balance_txn(txn: Transaction) -> bool: