diff --git a/django/http/multipartparser.py b/django/http/multipartparser.py
index 958b519dc3..526e161ae4 100644
--- a/django/http/multipartparser.py
+++ b/django/http/multipartparser.py
@@ -70,7 +70,7 @@ class MultiPartParser:
         ctypes, opts = parse_header(content_type.encode('ascii'))
         boundary = opts.get('boundary')
         if not boundary or not cgi.valid_boundary(boundary):
-            raise MultiPartParserError('Invalid boundary in multipart: %s' % boundary.decode())
+            raise MultiPartParserError('Invalid boundary in multipart: %s' % force_str(boundary))
 
         # Content-Length should contain the length of the body we are about
         # to receive.
diff --git a/tests/requests/tests.py b/tests/requests/tests.py
index 9391ca2a08..945d77ff6e 100644
--- a/tests/requests/tests.py
+++ b/tests/requests/tests.py
@@ -5,6 +5,7 @@ from urllib.parse import urlencode
 from django.core.exceptions import DisallowedHost
 from django.core.handlers.wsgi import LimitedStream, WSGIRequest
 from django.http import HttpRequest, RawPostDataException, UnreadablePostError
+from django.http.multipartparser import MultiPartParserError
 from django.http.request import HttpHeaders, split_domain_port
 from django.test import RequestFactory, SimpleTestCase, override_settings
 from django.test.client import FakePayload
@@ -476,6 +477,16 @@ class RequestsTests(SimpleTestCase):
         })
         self.assertFalse(request.POST._mutable)
 
+    def test_multipart_without_boundary(self):
+        request = WSGIRequest({
+            'REQUEST_METHOD': 'POST',
+            'CONTENT_TYPE': 'multipart/form-data;',
+            'CONTENT_LENGTH': 0,
+            'wsgi.input': FakePayload(),
+        })
+        with self.assertRaisesMessage(MultiPartParserError, 'Invalid boundary in multipart: None'):
+            request.POST
+
     def test_POST_connection_error(self):
         """
         If wsgi.input.read() raises an exception while trying to read() the