diff --git a/nylas/client/client.py b/nylas/client/client.py
index 6f7ab174..ab69f229 100644
--- a/nylas/client/client.py
+++ b/nylas/client/client.py
@@ -817,19 +817,19 @@ def _request(self, method, url, cls=None, headers=None, **kwargs):
 
     def _add_auth_header(self, auth_method):
         authorization = None
-        if auth_method is AuthMethod.BEARER:
+        if auth_method == AuthMethod.BEARER:
             authorization = (
                 "Bearer {token}".format(token=self.access_token)
                 if self.access_token
                 else None
             )
-        elif auth_method is AuthMethod.BASIC_CLIENT_ID_AND_SECRET:
+        elif auth_method == AuthMethod.BASIC_CLIENT_ID_AND_SECRET:
             if self.client_id and self.client_secret:
                 credential = "{client_id}:{client_secret}".format(
                     client_id=self.client_id, client_secret=self.client_secret
                 )
                 authorization = "Basic {credential}".format(
-                    credential=b64encode(credential.encode("utf8"))
+                    credential=b64encode(credential.encode("utf8")).decode("utf8")
                 )
         else:
             if self.client_secret:
diff --git a/tests/test_client.py b/tests/test_client.py
index 1eb6f4b8..82fed5a9 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -6,6 +6,7 @@
 import responses
 from nylas.client import APIClient
 from nylas.client.restful_models import Contact
+from nylas.utils import AuthMethod
 
 
 def urls_equal(url1, url2):
@@ -345,3 +346,22 @@ def test_count(mocked_responses, api_client, api_url):
 
     contact_count = api_client.contacts.count()
     assert contact_count == 721
+
+
+def test_add_auth_header_bearer(api_client):
+    api_client.access_token = "access_token"
+    auth_header = api_client._add_auth_header(AuthMethod.BEARER)
+    assert auth_header == {"Authorization": "Bearer access_token"}
+
+
+def test_add_auth_header_basic_client_id_and_secret(api_client):
+    api_client.client_id = "client_id"
+    api_client.client_secret = "client_secret"
+    auth_header = api_client._add_auth_header(AuthMethod.BASIC_CLIENT_ID_AND_SECRET)
+    assert auth_header == {"Authorization": "Basic Y2xpZW50X2lkOmNsaWVudF9zZWNyZXQ="}
+
+
+def test_add_auth_header_basic(api_client):
+    api_client.client_secret = "client_secret"
+    auth_header = api_client._add_auth_header(AuthMethod.BASIC)
+    assert auth_header == {"Authorization": "Basic Y2xpZW50X3NlY3JldDo="}