diff --git a/Adyen/client.py b/Adyen/client.py
index 8915f078..e8324854 100644
--- a/Adyen/client.py
+++ b/Adyen/client.py
@@ -611,7 +611,7 @@ def _handle_response(self, url, raw_response, raw_request,
         Returns:
             AdyenResult: Result object if successful.
         """
-        if (status_code != 200 and status_code !=  201):
+        if (status_code != 200 and status_code != 201):
             response = {}
             # If the result can't be parsed into json, most likely is raw html.
             # Some response are neither json or raw html, handle them here:
diff --git a/Adyen/util.py b/Adyen/util.py
index b9cb9520..4efe6243 100644
--- a/Adyen/util.py
+++ b/Adyen/util.py
@@ -35,6 +35,8 @@ def escape_val(val):
 
 
 def is_valid_hmac(dict_object, hmac_key):
+    dict_object = dict_object.copy()
+
     if 'additionalData' in dict_object:
         if dict_object['additionalData']['hmacSignature'] == "":
             raise ValueError("Must Provide hmacSignature in additionalData")
@@ -85,6 +87,8 @@ def escape_val(val):
 
 
 def is_valid_hmac_notification(dict_object, hmac_key):
+    dict_object = dict_object.copy()
+
     if 'additionalData' in dict_object:
         if dict_object['additionalData']['hmacSignature'] == "":
             raise ValueError("Must Provide hmacSignature in additionalData")
diff --git a/test/CheckoutTest.py b/test/CheckoutTest.py
index a94dd297..19d7bf42 100644
--- a/test/CheckoutTest.py
+++ b/test/CheckoutTest.py
@@ -497,4 +497,4 @@ def test_sessions_error(self):
         result = self.adyen.checkout.sessions(request)
         self.assertEqual(422, result.message['status'])
         self.assertEqual("130", result.message['errorCode'])
-        self.assertEqual("validation", result.message['errorType'])
\ No newline at end of file
+        self.assertEqual("validation", result.message['errorType'])
diff --git a/test/UtilTest.py b/test/UtilTest.py
index 9cd9b334..488c6c12 100644
--- a/test/UtilTest.py
+++ b/test/UtilTest.py
@@ -34,6 +34,9 @@ def test_hpp_request_item_hmac(self):
         self.assertEqual(hmac_calculation_str, expected_hmac)
         request['additionalData'] = {'hmacSignature': hmac_calculation_str}
         hmac_validate = is_valid_hmac(request, key)
+        self.assertIn('additionalData', request)
+        self.assertDictEqual(request['additionalData'],
+                             {'hmacSignature': hmac_calculation_str})
         self.assertTrue(hmac_validate)
 
     def test_notification_request_item_hmac(self):
@@ -49,9 +52,9 @@ def test_notification_request_item_hmac(self):
             "success": "true",
             "eventDate": "2019-05-06T17:15:34.121+02:00",
             "operations": [
-               "CANCEL",
-               "CAPTURE",
-               "REFUND"
+                "CANCEL",
+                "CAPTURE",
+                "REFUND"
             ],
             "paymentMethod": "visa",
         }
@@ -64,4 +67,7 @@ def test_notification_request_item_hmac(self):
         self.assertEqual(hmac_calculation_str, expected_hmac)
         request['additionalData'] = {'hmacSignature': hmac_calculation_str}
         hmac_validate = is_valid_hmac_notification(request, key)
+        self.assertIn('additionalData', request)
+        self.assertDictEqual(request['additionalData'],
+                             {'hmacSignature': hmac_calculation_str})
         self.assertTrue(hmac_validate)