diff --git a/daphne/cli.py b/daphne/cli.py
index f972a41..31cfe2d 100755
--- a/daphne/cli.py
+++ b/daphne/cli.py
@@ -136,23 +136,23 @@ class CommandLineInterface(object):
             action="store_true",
         )
         self._arg_proxy_host = self.parser.add_argument(
-            '--proxy-headers-host',
-            dest='proxy_headers_host',
-            help='Specify which header will be used for getting the host '
-            'part. Can be omitted, requires --proxy-headers to be specified '
-            'when passed. \'X-Real-IP\' (when passed by your webserver) is a '
-            'good candidate for this.',
+            "--proxy-headers-host",
+            dest="proxy_headers_host",
+            help="Specify which header will be used for getting the host "
+            "part. Can be omitted, requires --proxy-headers to be specified "
+            "when passed. \"X-Real-IP\" (when passed by your webserver) is a "
+            "good candidate for this.",
             default=False,
-            action='store',
+            action="store",
         )
         self._arg_proxy_port = self.parser.add_argument(
-            '--proxy-headers-port',
-            dest='proxy_headers_port',
-            help='Specify which header will be used for getting the port '
-            'part. Can be omitted, requires --proxy-headers to be specified '
-            'when passed.',
+            "--proxy-headers-port",
+            dest="proxy_headers_port",
+            help="Specify which header will be used for getting the port "
+            "part. Can be omitted, requires --proxy-headers to be specified "
+            "when passed.",
             default=False,
-            action='store',
+            action="store",
         )
         self.parser.add_argument(
             "application",
@@ -174,7 +174,7 @@ class CommandLineInterface(object):
             return
         raise ArgumentError(
             argument=argument,
-            message='--proxy-headers has to be passed for this parameter.')
+            message="--proxy-headers has to be passed for this parameter.")
 
     def _get_forwarded_host(self, args: Namespace) -> str_or_none:
         """
@@ -186,7 +186,7 @@ class CommandLineInterface(object):
                 argument=self._arg_proxy_host, args=args)
             return args.proxy_headers_host
         if args.proxy_headers:
-            return 'X-Forwarded-For'
+            return "X-Forwarded-For"
 
     def _get_forwarded_port(self, args: Namespace) -> str_or_none:
         """
@@ -198,7 +198,7 @@ class CommandLineInterface(object):
                 argument=self._arg_proxy_port, args=args)
             return args.proxy_headers_port
         if args.proxy_headers:
-            return 'X-Forwarded-Port'
+            return "X-Forwarded-Port"
 
     def run(self, args):
         """
diff --git a/daphne/utils.py b/daphne/utils.py
index 1c5b3db..00a25c5 100644
--- a/daphne/utils.py
+++ b/daphne/utils.py
@@ -46,11 +46,11 @@ def parse_x_forwarded_for(headers,
     new_headers = dict()
     for name, values in headers.items():
         name = name.lower()
-        name = name if type(name) is bytes else name.encode('utf-8')
+        name = name if type(name) is bytes else name.encode("utf-8")
         new_headers[name] = values
     headers = new_headers
 
-    address_header_name = address_header_name.lower().encode('utf-8')
+    address_header_name = address_header_name.lower().encode("utf-8")
     result = original
     if address_header_name in headers:
         address_value = header_value(headers, address_header_name)
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 61e468d..f946a82 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -243,9 +243,9 @@ class TestCLIInterface(TestCase):
         `X-Forwarded-For` header.
         """
         self.assertCLI(
-            ['--proxy-headers'],
+            ["--proxy-headers"],
             {
-                'proxy_forwarded_address_header': 'X-Forwarded-For',
+                "proxy_forwarded_address_header": "X-Forwarded-For",
             },
         )
 
@@ -255,22 +255,22 @@ class TestCLIInterface(TestCase):
         the passed one, and `--proxy-headers` is mandatory.
         """
         self.assertCLI(
-            ['--proxy-headers', '--proxy-headers-host', 'blah'],
+            ["--proxy-headers", "--proxy-headers-host", "blah"],
             {
-                'proxy_forwarded_address_header': 'blah',
+                "proxy_forwarded_address_header": "blah",
             },
         )
         with self.assertRaises(expected_exception=ArgumentError) as exc:
             self.assertCLI(
-                ['--proxy-headers-host', 'blah'],
+                ["--proxy-headers-host", "blah"],
                 {
-                    'proxy_forwarded_address_header': 'blah',
+                    "proxy_forwarded_address_header": "blah",
                 },
             )
-        self.assertEqual(exc.exception.argument_name, '--proxy-headers-host')
+        self.assertEqual(exc.exception.argument_name, "--proxy-headers-host")
         self.assertEqual(
             exc.exception.message,
-            '--proxy-headers has to be passed for this parameter.')
+            "--proxy-headers has to be passed for this parameter.")
 
     def test_custom_proxyport(self):
         """
@@ -278,19 +278,19 @@ class TestCLIInterface(TestCase):
         the passed one, and `--proxy-headers` is mandatory.
         """
         self.assertCLI(
-            ['--proxy-headers', '--proxy-headers-port', 'blah2'],
+            ["--proxy-headers", "--proxy-headers-port", "blah2"],
             {
-                'proxy_forwarded_port_header': 'blah2',
+                "proxy_forwarded_port_header": "blah2",
             },
         )
         with self.assertRaises(expected_exception=ArgumentError) as exc:
             self.assertCLI(
-                ['--proxy-headers-port', 'blah2'],
+                ["--proxy-headers-port", "blah2"],
                 {
-                    'proxy_forwarded_address_header': 'blah2',
+                    "proxy_forwarded_address_header": "blah2",
                 },
             )
-        self.assertEqual(exc.exception.argument_name, '--proxy-headers-port')
+        self.assertEqual(exc.exception.argument_name, "--proxy-headers-port")
         self.assertEqual(
             exc.exception.message,
-            '--proxy-headers has to be passed for this parameter.')
+            "--proxy-headers has to be passed for this parameter.")