diff --git a/laterpay/__init__.py b/laterpay/__init__.py
index c92f556..f2df4a4 100644
--- a/laterpay/__init__.py
+++ b/laterpay/__init__.py
@@ -421,10 +421,7 @@ class LaterPayClient(object):
         """
         params = self._sign_and_encode(params=params, url=url, method=method)
 
-        headers = {
-            'X-LP-APIVersion': 2,
-            'User-Agent': 'LaterPay Client - Python - v0.2'
-        }
+        headers = self.get_request_headers()
 
         if method == 'POST':
             req = Request(url, data=params, headers=headers)
@@ -503,7 +500,7 @@ class LaterPayClient(object):
         Return a ``dict`` of request headers to be sent to the API.
         """
         return {
-            'X-LP-APIVersion': 2,
+            'X-LP-APIVersion': '2',
             # TODO: Add client version information.
             'User-Agent': 'LaterPay Client Python',
         }

diff --git a/tests/test_client.py b/tests/test_client.py
index e6ebc1c..f3069e7 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -302,7 +302,7 @@ class TestLaterPayClient(unittest.TestCase):
 
         call = responses.calls[0]
 
-        self.assertEqual(call.request.headers['X-LP-APIVersion'], 2)
+        self.assertEqual(call.request.headers['X-LP-APIVersion'], '2')
 
         qd = parse_qs(urlparse(call.request.url).query)
 

python-requests requires string only headers
As of python-requests 2.11 headers that are neither string not bytes are not accepted anymore. See kennethreitz/requests#3477
tests/test_client.py::TestLaterPayClient::test_get_access_data_success
tests/test_client.py::TestLaterPayClient::test_get_add_url_with_use_dialog_api_false tests/test_client.py::TestLaterPayClient::test_get_login_dialog_url_without_use_dialog_api tests/test_client.py::TestLaterPayClient::test_get_logout_dialog_url_without_use_dialog_api tests/test_client.py::TestLaterPayClient::test_get_buy_url_with_use_dialog_api_false tests/test_client.py::TestLaterPayClient::test_get_controls_balance_url_all_set tests/test_client.py::TestLaterPayClient::test_get_controls_links_url_all_set_short tests/test_client.py::TestLaterPayClient::test_get_add_url_product_key_param tests/test_client.py::TestLaterPayClient::test_get_controls_links_url_all_defaults tests/test_client.py::TestLaterPayClient::test_transaction_reference tests/test_client.py::TestLaterPayClient::test_get_logout_dialog_url_with_use_dialog_api_false tests/test_client.py::TestLaterPayClient::test_get_signup_dialog_url_with_use_dialog_api_false tests/test_client.py::TestLaterPayClient::test_get_login_dialog_url_with_use_dialog_api_false tests/test_client.py::TestLaterPayClient::test_has_token tests/test_client.py::TestLaterPayClient::test_get_add_url_no_product_key_param tests/test_client.py::TestLaterPayClient::test_get_web_url_extra_kwargs tests/test_client.py::TestLaterPayClient::test_log_warning_for_skip_add_to_invoice_deprecation tests/test_client.py::TestLaterPayClient::test_get_buy_url_product_key_param tests/test_client.py::TestLaterPayClient::test_get_buy_url_no_product_key_param tests/test_client.py::TestLaterPayClient::test_get_signup_dialog_url_without_use_dialog_api tests/test_client.py::TestLaterPayClient::test_get_access_params tests/test_client.py::TestLaterPayClient::test_get_controls_links_url_all_set_long tests/test_client.py::TestLaterPayClient::test_failure_url_param tests/test_client.py::TestLaterPayClient::test_get_web_url_has_no_none_params tests/test_client.py::TestLaterPayClient::test_get_controls_balance_url_all_defaults tests/test_client.py::TestLaterPayClient::test_get_gettoken_redirect tests/test_client.py::TestItemDefinition::test_item_definition