diff --git a/gunicorn/http/wsgi.py b/gunicorn/http/wsgi.py
index 2ca242665..b8b56934b 100644
--- a/gunicorn/http/wsgi.py
+++ b/gunicorn/http/wsgi.py
@@ -317,7 +317,7 @@ def send_headers(self):
         tosend.extend(["%s: %s\r\n" % (k, v) for k, v in self.headers])
 
         header_str = "%s\r\n" % "".join(tosend)
-        util.write(self.sock, util.to_bytestring(header_str))
+        util.write(self.sock, util.to_latin1(header_str))
         self.headers_sent = True
 
     def write(self, arg):
diff --git a/gunicorn/util.py b/gunicorn/util.py
index efe5f3d8d..ad5dd3435 100644
--- a/gunicorn/util.py
+++ b/gunicorn/util.py
@@ -508,6 +508,15 @@ def to_bytestring(value):
     return value.encode("utf-8")
 
 
+def to_latin1(value):
+    """Converts a string argument to a byte string"""
+    if isinstance(value, bytes):
+        return value
+    if not isinstance(value, text_type):
+        raise TypeError('%r is not a string' % value)
+    return value.encode("latin-1")
+
+
 def is_fileobject(obj):
     if not hasattr(obj, "tell") or not hasattr(obj, "fileno"):
         return False
diff --git a/tests/test_http_body.py b/tests/test_http.py
similarity index 64%
rename from tests/test_http_body.py
rename to tests/test_http.py
index 151df8dde..1d5e4f197 100644
--- a/tests/test_http_body.py
+++ b/tests/test_http.py
@@ -1,6 +1,14 @@
+# -*- encoding: utf-8 -*-
+
 import t
+from gunicorn import util
 from gunicorn.http.body import Body
+from gunicorn.http.wsgi import Response
 from gunicorn.six import BytesIO
+try:
+    import unittest.mock as mock
+except ImportError:
+    import mock
 
 
 def assert_readline(payload, size, expected):
@@ -57,3 +65,23 @@ def test_readline_buffer_loaded_with_size():
     assert body.readline(2) == b"\n"
     assert body.readline(2) == b"de"
     assert body.readline(2) == b"f"
+
+
+def test_http_header_encoding():
+    """ tests whether http response headers are ISO-8859-1 encoded """
+
+    mocked_socket = mock.MagicMock()
+    mocked_socket.sendall = mock.MagicMock()
+    mocked_request = mock.MagicMock()
+    response = Response(mocked_request, mocked_socket, None)
+
+    # set umlaut header
+    response.headers.append(('foo', 'häder'))
+    response.send_headers()
+
+    # build our own header_str to compare against
+    tosend = response.default_headers()
+    tosend.extend(["%s: %s\r\n" % (k, v) for k, v in response.headers])
+    header_str = "%s\r\n" % "".join(tosend)
+
+    mocked_socket.sendall.assert_called_with(util.to_latin1(header_str))