diff --git a/gratipay/testing/billing.py b/gratipay/testing/billing.py
index 62b5b29c1e..cd6aeaf69b 100644
--- a/gratipay/testing/billing.py
+++ b/gratipay/testing/billing.py
@@ -49,6 +49,14 @@ def setUp(self):
                                            claimed_time='now', email_address='abcd@gmail.com')
         self.homer_route = ExchangeRoute.insert(self.homer, 'paypal', 'abcd@gmail.com')
 
+        # A customer with both Braintree and Paypal attached.
+        self.marge = self.make_participant('marge', is_suspicious=False, verified_in='US',
+                                           claimed_time='now', email_address='marge@example.com')
+        self.marge_paypal_route = ExchangeRoute.insert(self.marge, 'paypal', 'marge@example.com')
+        self.marge_braintree_route = ExchangeRoute.insert(self.marge, 'braintree-cc',
+                                                                               self.marge_cc_token)
+        self.marge_route = self.marge_paypal_route  # so hacky
+
 
     @classmethod
     def tearDownClass(cls):
@@ -66,9 +74,11 @@ def install_fixture():
         cls = BillingHarness
         cls.roman_bt_id = braintree.Customer.create().customer.id
         cls.obama_bt_id = braintree.Customer.create().customer.id
+        cls.marge_bt_id = braintree.Customer.create().customer.id
         cls.bt_card = braintree.PaymentMethod.create({
             "customer_id": cls.obama_bt_id,
             "payment_method_nonce": Nonces.Transactable
         }).payment_method
         cls.obama_cc_token = cls.bt_card.token
+        cls.marge_cc_token = cls.bt_card.token
         cls._fixture_installed = True
diff --git a/tests/py/test_billing_payday.py b/tests/py/test_billing_payday.py
index 785832adaa..49f7d23602 100644
--- a/tests/py/test_billing_payday.py
+++ b/tests/py/test_billing_payday.py
@@ -640,3 +640,62 @@ def test_it_notifies_participants(self):
             assert self.get_last_email()['to'] == 'kalel <kalel@example.net>'
             assert 'Gratiteam' in self.get_last_email()['body_text']
             assert 'Gratiteam' in self.get_last_email()['body_html']
+
+
+class TestNegativeBalances(BillingHarness):
+
+    def send_negative(self, username, new_balance):
+        # There are two ways to record an exchange:
+        #  - self.make_exchange -> gratipay.billing.record_exchange # disallows negative balances
+        #  - /~user/history/record-an-exchange                      # allows negative balances
+        self.make_participant('admin', claimed_time='now', is_admin=True).username
+        self.client.PxST( '/~{}/history/record-an-exchange'.format(username)
+                        , { 'amount': unicode(new_balance)
+                          , 'fee': '0'
+                          , 'note': 'overpayment!'
+                          , 'status': 'succeeded'
+                          , 'route_id': unicode(getattr(self, username + '_route').id)
+                           }
+                        , auth_as='admin'
+                         )  # responds with 302
+        assert P(username).balance == new_balance
+
+    def ncharges(self, username):
+        return self.db.one("""
+
+            SELECT count(*)
+              FROM exchanges e
+              JOIN exchange_routes er
+                ON e.route = er.id
+             WHERE er.network='braintree-cc'
+               AND e.participant=%s
+               AND e.amount > 0
+
+        """, (username,))
+
+    def team_for(self, participant):
+        team = self.make_team(owner=participant, is_approved=True)
+        self.obama.set_payment_instruction(team, '20.00')
+
+    def run_returning_balance(self, username):
+        self.send_negative(username, -10)
+        self.run_payday()
+        assert self.ncharges(username) == 0
+        return P(username).balance
+
+
+    # nb - negative balance
+
+    def test_nb_stays_negative_when_no_card_attached_and_no_taking(self):
+        assert self.run_returning_balance('homer') == -10
+
+    def test_nb_stays_negative_even_when_card_attached_and_no_taking(self):
+        assert self.run_returning_balance('obama') == -10
+
+    def test_nb_increases_when_no_card_attached_and_taking(self):
+        self.team_for(self.homer)
+        assert self.run_returning_balance('homer') == 10
+
+    def test_nb_increase_comes_from_taking_and_not_card(self):
+        self.team_for(self.marge)
+        assert self.run_returning_balance('marge') == 10