diff --git a/websockets/client.py b/websockets/client.py
index 9aea4f6b7..411cf37f5 100644
--- a/websockets/client.py
+++ b/websockets/client.py
@@ -5,11 +5,10 @@
 
 import asyncio
 import collections.abc
-import http.client
 
 from .exceptions import InvalidHandshake, InvalidMessage
 from .handshake import build_request, check_response
-from .http import USER_AGENT, read_response
+from .http import USER_AGENT, build_headers, read_response
 from .protocol import CONNECTING, OPEN, WebSocketCommonProtocol
 from .uri import parse_uri
 
@@ -35,8 +34,7 @@ def write_http_request(self, path, headers):
 
         """
         self.path = path
-        self.request_headers = http.client.HTTPMessage()
-        self.request_headers._headers = headers     # HACK
+        self.request_headers = build_headers(headers)
         self.raw_request_headers = headers
 
         # Since the path and headers only contain ASCII characters,
@@ -62,8 +60,7 @@ def read_http_response(self):
         except ValueError as exc:
             raise InvalidMessage("Malformed HTTP message") from exc
 
-        self.response_headers = http.client.HTTPMessage()
-        self.response_headers._headers = headers    # HACK
+        self.response_headers = build_headers(headers)
         self.raw_response_headers = headers
 
         return status_code, self.response_headers
diff --git a/websockets/http.py b/websockets/http.py
index 48ec2f5e8..e71e8c78d 100644
--- a/websockets/http.py
+++ b/websockets/http.py
@@ -8,6 +8,7 @@
 """
 
 import asyncio
+import http.client
 import re
 import sys
 
@@ -191,3 +192,15 @@ def read_line(stream):
     if not line.endswith(b'\r\n'):
         raise ValueError("Line without CRLF")
     return line
+
+
+def build_headers(raw_headers):
+    """
+    Build a date structure for HTTP headers from a list of name - value pairs.
+
+    See also https://github.com/aaugustin/websockets/issues/210.
+
+    """
+    headers = http.client.HTTPMessage()
+    headers._headers = raw_headers  # HACK
+    return headers
diff --git a/websockets/server.py b/websockets/server.py
index f4da5c59f..43a9c682b 100644
--- a/websockets/server.py
+++ b/websockets/server.py
@@ -6,13 +6,13 @@
 
 import asyncio
 import collections.abc
-import http.client
+import http
 import logging
 
 from .compatibility import asyncio_ensure_future
 from .exceptions import InvalidHandshake, InvalidMessage, InvalidOrigin
 from .handshake import build_response, check_request
-from .http import USER_AGENT, read_request
+from .http import USER_AGENT, build_headers, read_request
 from .protocol import CONNECTING, OPEN, WebSocketCommonProtocol
 
 
@@ -154,8 +154,7 @@ def read_http_request(self):
             raise InvalidMessage("Malformed HTTP message") from exc
 
         self.path = path
-        self.request_headers = http.client.HTTPMessage()
-        self.request_headers._headers = headers     # HACK
+        self.request_headers = build_headers(headers)
         self.raw_request_headers = headers
 
         return path, self.request_headers
@@ -166,8 +165,7 @@ def write_http_response(self, status, headers):
         Write status line and headers to the HTTP response.
 
         """
-        self.response_headers = http.client.HTTPMessage()
-        self.response_headers._headers = headers    # HACK
+        self.response_headers = build_headers(headers)
         self.raw_response_headers = headers
 
         # Since the status line and headers only contain ASCII characters,
diff --git a/websockets/test_http.py b/websockets/test_http.py
index 8035451c7..ff2fc0a76 100644
--- a/websockets/test_http.py
+++ b/websockets/test_http.py
@@ -2,10 +2,10 @@
 import unittest
 
 from .http import *
-from .http import read_headers  # private API
+from .http import build_headers, read_headers  # private APIs
 
 
-class HTTPTests(unittest.TestCase):
+class HTTPAsyncTests(unittest.TestCase):
 
     def setUp(self):
         super().setUp()
@@ -97,3 +97,31 @@ def test_line_ending(self):
         self.stream.feed_data(b'foo: bar\n\n')
         with self.assertRaises(ValueError):
             self.loop.run_until_complete(read_headers(self.stream))
+
+
+class HTTPSyncTests(unittest.TestCase):
+
+    def test_build_headers(self):
+        headers = build_headers([
+            ('X-Foo', 'Bar'),
+            ('X-Baz', 'Quux Quux'),
+        ])
+
+        self.assertEqual(headers['X-Foo'], 'Bar')
+        self.assertEqual(headers['X-Bar'], None)
+
+        self.assertEqual(headers.get('X-Bar', ''), '')
+        self.assertEqual(headers.get('X-Baz', ''), 'Quux Quux')
+
+    def test_build_headers_multi_value(self):
+        headers = build_headers([
+            ('X-Foo', 'Bar'),
+            ('X-Foo', 'Baz'),
+        ])
+
+        # Getting a single value is non-deterministic.
+        self.assertIn(headers['X-Foo'], ['Bar', 'Baz'])
+        self.assertIn(headers.get('X-Foo'), ['Bar', 'Baz'])
+
+        # Ordering is deterministic when getting all values.
+        self.assertEqual(headers.get_all('X-Foo'), ['Bar', 'Baz'])