diff --git a/eopayment/__init__.py b/eopayment/__init__.py
index 245c5e2..aab050f 100644
--- a/eopayment/__init__.py
+++ b/eopayment/__init__.py
@@ -164,8 +164,9 @@ class Payment(object):
             kwargs['capture_day'] = capture_day
 
         for param in kwargs:
-            # encode all input params to unicode
-            kwargs[param] = force_text(kwargs[param])
+            # encode all but bool input params to unicode
+            if not isinstance(kwargs[param], bool):
+                kwargs[param] = force_text(kwargs[param])
         return self.backend.request(amount, **kwargs)
 
     def response(self, query_string, **kwargs):
diff --git a/tests/test_paybox.py b/tests/test_paybox.py
index 577825e..c251322 100644
--- a/tests/test_paybox.py
+++ b/tests/test_paybox.py
@@ -85,7 +85,7 @@ class PayboxTests(TestCase):
         amount = '19.99'
         transaction_id, kind, what = backend.request(
             Decimal(amount), email=email, orderid=order_id,
-            transaction_id=transaction, time=time)
+            transaction_id=transaction, time=time, manual_validation=False)
         self.assertEqual(kind, eopayment.FORM)
         self.assertEqual(transaction_id, '1234')
         root = ET.fromstring(str(what))
diff --git a/tests/test_systempayv2.py b/tests/test_systempayv2.py
index 6dcb29f..240f936 100644
--- a/tests/test_systempayv2.py
+++ b/tests/test_systempayv2.py
@@ -143,3 +143,7 @@ def test_manual_validation():
     data['manual_validation'] = True
     transaction_id, f, form = backend.request(**data.copy())
     assert get_field(form, 'vads_validation_mode')['value'] == '1'
+
+    data['manual_validation'] = False
+    transaction_id, f, form = backend.request(**data.copy())
+    assert get_field(form, 'vads_validation_mode')['value'] == ''