diff --git a/django/utils/http.py b/django/utils/http.py
index 2375f95b5b..aa6d56d34a 100644
--- a/django/utils/http.py
+++ b/django/utils/http.py
@@ -10,7 +10,7 @@ from binascii import Error as BinasciiError
 from email.utils import formatdate
 
 from django.utils.datastructures import MultiValueDict
-from django.utils.encoding import force_str, force_text
+from django.utils.encoding import force_bytes, force_str, force_text
 from django.utils.functional import allow_lazy
 from django.utils import six
 from django.utils.six.moves.urllib.parse import (
@@ -227,7 +227,7 @@ def urlsafe_base64_decode(s):
     Decodes a base64 encoded string, adding back any trailing equal signs that
     might have been stripped.
     """
-    s = s.encode('utf-8')  # base64encode should only return ASCII.
+    s = force_bytes(s)
     try:
         return base64.urlsafe_b64decode(s.ljust(len(s) + len(s) % 4, b'='))
     except (LookupError, BinasciiError) as e:
diff --git a/tests/utils_tests/test_http.py b/tests/utils_tests/test_http.py
index 3f512ad80b..db24d1c9f2 100644
--- a/tests/utils_tests/test_http.py
+++ b/tests/utils_tests/test_http.py
@@ -119,6 +119,12 @@ class TestUtilsHttp(unittest.TestCase):
                      '/url%20with%20spaces/'):
             self.assertTrue(http.is_safe_url(good_url, host='testserver'), "%s should be allowed" % good_url)
 
+    def test_urlsafe_base64_roundtrip(self):
+        bytestring = b'foo'
+        encoded = http.urlsafe_base64_encode(bytestring)
+        decoded = http.urlsafe_base64_decode(encoded)
+        self.assertEqual(bytestring, decoded)
+
 
 class ETagProcessingTests(unittest.TestCase):
     def test_parsing(self):