diff --git a/requests_http_signature/__init__.py b/requests_http_signature/__init__.py
index 9ebb4d6..b7336d7 100644
--- a/requests_http_signature/__init__.py
+++ b/requests_http_signature/__init__.py
@@ -98,7 +98,7 @@ class HTTPSignatureAuth(requests.auth.AuthBase):
         self.add_date(request)
         self.add_digest(request)
         raw_sig = Crypto(self.algorithm).sign(string_to_sign=self.get_string_to_sign(request, self.headers),
-                                              key=self.key,
+                                              key=self.key.encode() if isinstance(self.key, str) else self.key,
                                               passphrase=self.passphrase)
         sig = base64.b64encode(raw_sig).decode()
         sig_struct = [("keyId", self.key_id),
diff --git a/test/test.py b/test/test.py
index c7f0d25..b08c016 100755
--- a/test/test.py
+++ b/test/test.py
@@ -43,6 +43,12 @@ class TestRequestsHTTPSignature(unittest.TestCase):
         self.session = requests.Session()
         self.session.mount("http://", TestAdapter(self))
 
+    def test_readme_example(self):
+        preshared_key_id = 'squirrel'
+        preshared_secret = 'monorail_cat'
+        url = 'http://example.com/path'
+        requests.get(url, auth=HTTPSignatureAuth(key=preshared_secret, key_id=preshared_key_id))
+
     def test_basic_statements(self):
         url = 'http://example.com/path?query#fragment'
         self.session.get(url, auth=HTTPSignatureAuth(key=hmac_secret, key_id="sekret"))