diff --git a/django/http/response.py b/django/http/response.py
index 822589fe81..5cdedeca49 100644
--- a/django/http/response.py
+++ b/django/http/response.py
@@ -2,6 +2,7 @@ from __future__ import unicode_literals
 
 import datetime
 import time
+import sys
 from email.header import Header
 try:
     from urllib.parse import urlparse
@@ -160,7 +161,7 @@ class HttpResponseBase(six.Iterator):
         except UnicodeError as e:
             if mime_encode:
                 # Wrapping in str() is a workaround for #12422 under Python 2.
-                value = str(Header(value, 'utf-8').encode())
+                value = str(Header(value, 'utf-8', maxlinelen=sys.maxsize).encode())
             else:
                 e.reason += ', HTTP response headers must be in %s format' % charset
                 raise
diff --git a/tests/httpwrappers/tests.py b/tests/httpwrappers/tests.py
index 356818d2ef..0d9611ef0e 100644
--- a/tests/httpwrappers/tests.py
+++ b/tests/httpwrappers/tests.py
@@ -290,6 +290,13 @@ class HttpResponseTests(unittest.TestCase):
         self.assertRaises(UnicodeError, r.__setitem__, 'føø', 'bar')
         self.assertRaises(UnicodeError, r.__setitem__, 'føø'.encode('utf-8'), 'bar')
 
+    def test_long_line(self):
+        # Bug #20889: long lines trigger newlines to be added to headers
+        # (which is not allowed due to bug #10188)
+        h = HttpResponse()
+        f = 'zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz a\xcc\x88'.encode('latin-1')
+        f = f.decode('utf-8')
+        h['Content-Disposition'] = u'attachment; filename="%s"' % f
 
     def test_newlines_in_headers(self):
         # Bug #10188: Do not allow newlines in headers (CR or LF)