diff --git a/conservancy_beancount/data.py b/conservancy_beancount/data.py
index b93a2c7..7c016e0 100644
--- a/conservancy_beancount/data.py
+++ b/conservancy_beancount/data.py
@@ -25,6 +25,7 @@ import operator
 
 from beancount.core import account as bc_account
 from beancount.core import amount as bc_amount
+from beancount.core import convert as bc_convert
 
 from typing import (
     cast,
@@ -257,18 +258,28 @@ class Posting(BasePosting):
 
 def balance_of(txn: Transaction,
                *preds: Callable[[Account], Optional[bool]],
-) -> decimal.Decimal:
+) -> Amount:
     """Return the balance of specified postings in a transaction.
 
     Given a transaction and a series of account predicates, balance_of
     returns the balance of the amounts of all postings with accounts that
     match any of the predicates.
+
+    balance_of uses the "weight" of each posting, so the return value will
+    use the currency of the postings' cost when available.
     """
-    return sum(
-        (post.units.number for post in iter_postings(txn)
-         if any(pred(post.account) for pred in preds)),
-        decimal.Decimal(0),
-    )
+    match_posts = [post for post in iter_postings(txn)
+                   if any(pred(post.account) for pred in preds)]
+    number = decimal.Decimal(0)
+    if not match_posts:
+        currency = ''
+    else:
+        weights: Sequence[Amount] = [
+            bc_convert.get_weight(post) for post in match_posts  # type:ignore[no-untyped-call]
+        ]
+        number = sum((wt.number for wt in weights), number)
+        currency = weights[0].currency
+    return Amount._make((number, currency))
 
 def iter_postings(txn: Transaction) -> Iterator[Posting]:
     """Yield an enhanced Posting object for every posting in the transaction"""
diff --git a/conservancy_beancount/plugin/meta_approval.py b/conservancy_beancount/plugin/meta_approval.py
index ca09b4b..31fdc88 100644
--- a/conservancy_beancount/plugin/meta_approval.py
+++ b/conservancy_beancount/plugin/meta_approval.py
@@ -40,7 +40,7 @@ class MetaApproval(core._RequireLinksPostingMetadataHook):
                 txn,
                 data.Account.is_cash_equivalent,
                 data.Account.is_credit_card,
-            )
+            ).number
         )
 
     def _run_on_post(self, txn: Transaction, post: data.Posting) -> bool:
diff --git a/tests/test_data_balance_of.py b/tests/test_data_balance_of.py
index 91e63b7..6a44fd6 100644
--- a/tests/test_data_balance_of.py
+++ b/tests/test_data_balance_of.py
@@ -24,6 +24,7 @@ from . import testutil
 from conservancy_beancount import data
 
 is_cash_eq = data.Account.is_cash_equivalent
+USD = testutil.Amount
 
 @pytest.fixture
 def payable_payment_txn():
@@ -34,6 +35,14 @@ def payable_payment_txn():
         ('Assets:Checking', -5),
     ])
 
+@pytest.fixture
+def fx_donation_txn():
+    return testutil.Transaction(postings=[
+        ('Income:Donations', -500, 'EUR', ('.9', 'USD')),
+        ('Assets:Checking', 445),
+        ('Expenses:BankingFees', 5),
+    ])
+
 def balance_under(txn, *accts):
     pred = methodcaller('is_under', *accts)
     return data.balance_of(txn, pred)
@@ -43,17 +52,18 @@ def test_balance_of_simple_txn():
         ('Assets:Cash', 50),
         ('Income:Donations', -50),
     ])
-    assert balance_under(txn, 'Assets') == 50
-    assert balance_under(txn, 'Income') == -50
+    assert balance_under(txn, 'Assets') == USD(50)
+    assert balance_under(txn, 'Income') == USD(-50)
 
 def test_zero_balance_of(payable_payment_txn):
-    assert balance_under(payable_payment_txn, 'Equity') == 0
-    assert balance_under(payable_payment_txn, 'Assets:Cash') == 0
-    assert balance_under(payable_payment_txn, 'Liabilities:CreditCard') == 0
+    expected = testutil.Amount(0, '')
+    assert balance_under(payable_payment_txn, 'Equity') == expected
+    assert balance_under(payable_payment_txn, 'Assets:Cash') == expected
+    assert balance_under(payable_payment_txn, 'Liabilities:CreditCard') == expected
 
 def test_nonzero_balance_of(payable_payment_txn):
-    assert balance_under(payable_payment_txn, 'Assets', 'Expenses') == -50
-    assert balance_under(payable_payment_txn, 'Assets', 'Liabilities') == -5
+    assert balance_under(payable_payment_txn, 'Assets', 'Expenses') == USD(-50)
+    assert balance_under(payable_payment_txn, 'Assets', 'Liabilities') == USD(-5)
 
 def test_multiarg_balance_of():
     txn = testutil.Transaction(postings=[
@@ -61,7 +71,12 @@ def test_multiarg_balance_of():
         ('Expenses:BankingFees', 5),
         ('Assets:Checking', -655),
     ])
-    assert data.balance_of(txn, is_cash_eq, data.Account.is_credit_card) == -5
+    assert data.balance_of(txn, is_cash_eq, data.Account.is_credit_card) == USD(-5)
 
 def test_balance_of_multipost_txn(payable_payment_txn):
-    assert data.balance_of(payable_payment_txn, is_cash_eq) == -55
+    assert data.balance_of(payable_payment_txn, is_cash_eq) == USD(-55)
+
+def test_balance_of_multicurrency_txn(fx_donation_txn):
+    assert balance_under(fx_donation_txn, 'Income') == USD(-450)
+    assert balance_under(fx_donation_txn, 'Income', 'Assets') == USD(-5)
+    assert balance_under(fx_donation_txn, 'Income', 'Expenses') == USD(-445)
diff --git a/tests/testutil.py b/tests/testutil.py
index 583de75..c1b4580 100644
--- a/tests/testutil.py
+++ b/tests/testutil.py
@@ -69,16 +69,19 @@ def test_path(s):
 def Amount(number, currency='USD'):
     return bc_amount.Amount(Decimal(number), currency)
 
+def Cost(number, currency='USD', date=FY_MID_DATE, label=None):
+    return bc_data.Cost(Decimal(number), currency, date, label)
+
 def Posting(account, number,
             currency='USD', cost=None, price=None, flag=None,
             **meta):
-    if not (number is None or isinstance(number, Decimal)):
-        number = Decimal(number)
+    if cost is not None:
+        cost = Cost(*cost)
     if meta is None:
         meta = None
     return bc_data.Posting(
         account,
-        bc_amount.Amount(number, currency),
+        Amount(number, currency),
         cost,
         price,
         flag,