diff --git a/eopayment/__init__.py b/eopayment/__init__.py
index 95ec008..52c7061 100644
--- a/eopayment/__init__.py
+++ b/eopayment/__init__.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 
-from common import URL, HTML, FORM, RECEIVED, ACCEPTED, PAID, DENIED, CANCELED, CANCELLED, ERROR
+from common import (URL, HTML, FORM, RECEIVED, ACCEPTED, PAID, DENIED,
+                    CANCELED, CANCELLED, ERROR, ResponseError)
 
 __all__ = ['Payment', 'URL', 'HTML', 'FORM', 'SIPS',
 'SYSTEMPAY', 'SPPLUS', 'TIPI', 'DUMMY', 'get_backend', 'RECEIVED', 'ACCEPTED',
diff --git a/eopayment/common.py b/eopayment/common.py
index e421878..0a5881f 100644
--- a/eopayment/common.py
+++ b/eopayment/common.py
@@ -27,6 +27,10 @@ ERROR = 99
 ORDERID_TRANSACTION_SEPARATOR = '!'
 
 
+class ResponseError(Exception):
+    pass
+
+
 class PaymentResponse(object):
     '''Holds a generic view on the result of payment transaction response.
 
diff --git a/eopayment/dummy.py b/eopayment/dummy.py
index 7c2db23..3c02f14 100644
--- a/eopayment/dummy.py
+++ b/eopayment/dummy.py
@@ -10,7 +10,7 @@ try:
 except ImportError:
     from urlparse import parse_qs
 
-from common import PaymentCommon, URL, PaymentResponse, PAID, ERROR
+from common import PaymentCommon, URL, PaymentResponse, PAID, ERROR, ResponseError
 
 __all__ = [ 'Payment' ]
 
@@ -122,6 +122,8 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, logger=LOGGER, **kwargs):
         form = parse_qs(query_string)
+        if not 'transaction_id' in form:
+            raise ResponseError()
         transaction_id = form.get('transaction_id',[''])[0]
         form[self.BANK_ID] = transaction_id
 
diff --git a/eopayment/ogone.py b/eopayment/ogone.py
index e6a65e4..0872a34 100644
--- a/eopayment/ogone.py
+++ b/eopayment/ogone.py
@@ -5,7 +5,8 @@ import urlparse
 from decimal import Decimal, ROUND_HALF_UP
 
 from common import (PaymentCommon, PaymentResponse, FORM, CANCELLED, PAID,
-        ERROR, Form, DENIED, ACCEPTED, ORDERID_TRANSACTION_SEPARATOR)
+        ERROR, Form, DENIED, ACCEPTED, ORDERID_TRANSACTION_SEPARATOR,
+        ResponseError)
 def N_(message): return message
 
 ENVIRONMENT_TEST = 'TEST'
@@ -528,6 +529,8 @@ class Payment(PaymentCommon):
     def response(self, query_string, **kwargs):
         params = urlparse.parse_qs(query_string, True)
         params = dict((key.upper(), params[key][0]) for key in params)
+        if not set(params) >= set(['ORDERID', 'PAYID', 'STATUS', 'NCERROR']):
+            raise ResponseError()
         reference = params['ORDERID']
         transaction_id = params['PAYID']
         status = params['STATUS']
diff --git a/eopayment/paybox.py b/eopayment/paybox.py
index a6973ae..2ebed40 100644
--- a/eopayment/paybox.py
+++ b/eopayment/paybox.py
@@ -17,7 +17,7 @@ import string
 import warnings
 
 from common import (PaymentCommon, PaymentResponse, FORM, PAID, ERROR, Form,
-        ORDERID_TRANSACTION_SEPARATOR)
+        ORDERID_TRANSACTION_SEPARATOR, ResponseError)
 
 __all__ = ['sign', 'Payment']
 
@@ -253,6 +253,8 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, callback=False, **kwargs):
         d = urlparse.parse_qs(query_string, True, False)
+        if not set(d) >= set(['erreur', 'reference']):
+            raise ResponseError()
         signed = False
         if 'signature' in d:
             sig = d['signature'][0]
diff --git a/eopayment/sips.py b/eopayment/sips.py
index 301d414..ef5f1c6 100644
--- a/eopayment/sips.py
+++ b/eopayment/sips.py
@@ -9,7 +9,7 @@ import os.path
 import uuid
 import warnings
 
-from common import PaymentCommon, HTML, PaymentResponse
+from common import PaymentCommon, HTML, PaymentResponse, ResponseError
 from cb import CB_RESPONSE_CODES
 
 '''
@@ -159,6 +159,8 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, **kwargs):
         form = urlparse.parse_qs(query_string)
+        if not DATA in form:
+            raise ResponseError()
         params = {'message': form[DATA][0]}
         result = self.execute('response', params)
         d = dict(zip(RESPONSE_PARAMS, result))
diff --git a/eopayment/sips2.py b/eopayment/sips2.py
index f2f4620..1a99571 100644
--- a/eopayment/sips2.py
+++ b/eopayment/sips2.py
@@ -8,7 +8,8 @@ import hashlib
 from gettext import gettext as _
 import warnings
 
-from common import PaymentCommon, FORM, Form, PaymentResponse, PAID, ERROR, CANCELED
+from common import (PaymentCommon, FORM, Form, PaymentResponse, PAID, ERROR,
+        CANCELED, ResponseError)
 
 __all__ = ['Payment']
 
@@ -190,10 +191,9 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, **kwargs):
         form = urlparse.parse_qs(query_string)
+        if not set(form) >= set(['Data', 'Seal', 'InterfaceVersion']):
+            raise ResponseError()
         self.logger.debug('received query string %r', form)
-        assert 'Data' in form
-        assert 'Seal' in form
-        assert 'InterfaceVersion' in form
         data = self.decode_data(form['Data'][0])
         seal = form['Seal'][0]
         self.logger.debug('parsed response %r seal %r', data, seal)
diff --git a/eopayment/spplus.py b/eopayment/spplus.py
index af3136a..d6e7b48 100644
--- a/eopayment/spplus.py
+++ b/eopayment/spplus.py
@@ -14,7 +14,7 @@ import warnings
 
 import Crypto.Cipher.DES
 from common import (PaymentCommon, URL, PaymentResponse, RECEIVED, ACCEPTED,
-        PAID, ERROR)
+        PAID, ERROR, ResponseError)
 
 def N_(message): return message
 
@@ -176,6 +176,8 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, logger=LOGGER, **kwargs):
         form = urlparse.parse_qs(query_string)
+        if not set(form) >= set([REFERENCE, ETAT, REFSFP]):
+            raise ResponseError()
         for key, value in form.iteritems():
             form[key] = value[0]
         logger.debug('received query_string %s' % query_string)
diff --git a/eopayment/systempayv2.py b/eopayment/systempayv2.py
index 4442668..bb1412a 100644
--- a/eopayment/systempayv2.py
+++ b/eopayment/systempayv2.py
@@ -8,7 +8,8 @@ import urlparse
 import warnings
 from gettext import gettext as _
 
-from common import PaymentCommon, PaymentResponse, PAID, ERROR, FORM, Form
+from common import (PaymentCommon, PaymentResponse, PAID, ERROR, FORM, Form,
+                    ResponseError)
 from cb import CB_RESPONSE_CODES
 
 __all__ = ['Payment']
@@ -338,6 +339,8 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, **kwargs):
         fields = urlparse.parse_qs(query_string, True)
+        if not set(fields) >= set([SIGNATURE, VADS_CTX_MODE, VADS_AUTH_RESULT]):
+            raise ResponseError()
         for key, value in fields.iteritems():
             fields[key] = value[0]
         copy = fields.copy()
diff --git a/eopayment/tipi.py b/eopayment/tipi.py
index 0342965..13f6fd0 100644
--- a/eopayment/tipi.py
+++ b/eopayment/tipi.py
@@ -2,7 +2,7 @@
 
 from decimal import Decimal, ROUND_DOWN
 from common import (PaymentCommon, PaymentResponse, URL, PAID, DENIED,
-        CANCELLED, ERROR)
+        CANCELLED, ERROR, ResponseError)
 from urllib import urlencode
 from urlparse import parse_qs
 from gettext import gettext as _
@@ -136,6 +136,8 @@ class Payment(PaymentCommon):
 
     def response(self, query_string, **kwargs):
         fields = parse_qs(query_string, True)
+        if not set(fields) >= set(['refdet', 'resultrans']):
+            raise ResponseError()
         for key, value in fields.iteritems():
             fields[key] = value[0]
         refdet = fields.get('refdet')
diff --git a/tests/test_ogone.py b/tests/test_ogone.py
index ee210dd..5108223 100644
--- a/tests/test_ogone.py
+++ b/tests/test_ogone.py
@@ -3,6 +3,7 @@ import urllib
 
 import eopayment
 import eopayment.ogone as ogone
+from eopayment import ResponseError
 
 PSPID = '2352566'
 
@@ -52,3 +53,10 @@ class OgoneTests(TestCase):
                 'payid': '32100123', 'status': 9, 'ncerror': 0}
         response = ogone_backend.response(urllib.urlencode(data))
         self.assertEqual(response.order_id, order_id)
+
+    def test_bad_response(self):
+        ogone_backend = eopayment.Payment('ogone', BACKEND_PARAMS)
+        order_id = 'myorder'
+        data = {'payid': '32100123', 'status': 9, 'ncerror': 0}
+        with self.assertRaises(ResponseError):
+            response = ogone_backend.response(urllib.urlencode(data))