diff --git a/django/middleware/common.py b/django/middleware/common.py
index dad1e6b2eb8..68fcb8a7802 100644
--- a/django/middleware/common.py
+++ b/django/middleware/common.py
@@ -127,7 +127,7 @@ class BrokenLinkEmailsMiddleware(object):
             referer = force_text(request.META.get('HTTP_REFERER', ''), errors='replace')
 
             if not self.is_ignorable_request(request, path, domain, referer):
-                ua = request.META.get('HTTP_USER_AGENT', '<none>')
+                ua = force_text(request.META.get('HTTP_USER_AGENT', '<none>'), errors='replace')
                 ip = request.META.get('REMOTE_ADDR', '<none>')
                 mail_managers(
                     "Broken %slink on %s" % (
diff --git a/tests/middleware/tests.py b/tests/middleware/tests.py
index 3533b1d957a..8b20a0c627c 100644
--- a/tests/middleware/tests.py
+++ b/tests/middleware/tests.py
@@ -320,6 +320,16 @@ class BrokenLinkEmailsMiddlewareTest(TestCase):
         BrokenLinkEmailsMiddleware().process_response(self.req, self.resp)
         self.assertEqual(len(mail.outbox), 1)
 
+    @skipIf(six.PY3, "HTTP_USER_AGENT is str type on Python 3")
+    def test_404_error_nonascii_user_agent(self):
+        # Such user agent strings should not happen, but anyway, if it happens,
+        # let's not crash
+        self.req.META['HTTP_REFERER'] = '/another/url/'
+        self.req.META['HTTP_USER_AGENT'] = b'\xd0\xbb\xd0\xb8\xff\xff'
+        BrokenLinkEmailsMiddleware().process_response(self.req, self.resp)
+        self.assertEqual(len(mail.outbox), 1)
+        self.assertIn('User agent: \u043b\u0438\ufffd\ufffd\n', mail.outbox[0].body)
+
     def test_custom_request_checker(self):
         class SubclassedMiddleware(BrokenLinkEmailsMiddleware):
             ignored_user_agent_patterns = (re.compile(r'Spider.*'),