diff --git a/application/account_facts_publisher.py b/application/account_facts_publisher.py
index 68ed7c8..5e24af5 100644
--- a/application/account_facts_publisher.py
+++ b/application/account_facts_publisher.py
@@ -191,6 +191,10 @@ def build_firstrade_account_snapshot(
     if not isinstance(balances, Mapping):
         raise AccountFactsPublishError("snapshot_invalid")
     currency = balances.get("currency")
+    # Firstrade US equity balance payloads often omit an ISO currency field; the
+    # rest of this platform already treats Firstrade cash as USD.
+    if currency is None:
+        currency = "USD"
     if not isinstance(currency, str) or not _CURRENCY_RE.fullmatch(currency):
         raise AccountFactsPublishError("provider_currency_unavailable")
     provider_equity = balances.get("provider_equity")
diff --git a/tests/test_account_facts_publisher.py b/tests/test_account_facts_publisher.py
index a725ea7..127e5ae 100644
--- a/tests/test_account_facts_publisher.py
+++ b/tests/test_account_facts_publisher.py
@@ -73,8 +73,17 @@ def test_builds_fixed_snapshot_with_only_provider_equity_and_cash():
     assert "buying_power" not in repr(payload)
 
 
-@pytest.mark.parametrize("value", [None, "", "usd", "US", "USDX", "USD " ])
-def test_rejects_missing_or_invalid_provider_currency(value):
+def test_defaults_missing_provider_currency_to_usd():
+    data = observation()
+    data["balances"]["currency"] = None
+    payload = build_firstrade_account_snapshot(
+        data, load_account_facts_publish_config(config()), account_scope="us"
+    )
+    assert payload["broker_reported_balances"][0]["currency"] == "USD"
+
+
+@pytest.mark.parametrize("value", ["", "usd", "US", "USDX", "USD "])
+def test_rejects_invalid_provider_currency(value):
     data = observation()
     data["balances"]["currency"] = value