diff --git a/rest_framework/utils/mediatypes.py b/rest_framework/utils/mediatypes.py
index def4b9641..865c283cc 100644
--- a/rest_framework/utils/mediatypes.py
+++ b/rest_framework/utils/mediatypes.py
@@ -49,10 +49,8 @@ def order_by_precedence(media_type_lst):
 @python_2_unicode_compatible
 class _MediaType(object):
     def __init__(self, media_type_str):
-        if media_type_str is None:
-            media_type_str = ''
-        self.orig = media_type_str
-        self.full_type, self.params = parse_header(media_type_str.encode(HTTP_HEADER_ENCODING))
+        self.orig = '' if (media_type_str is None) else media_type_str
+        self.full_type, self.params = parse_header(self.orig.encode(HTTP_HEADER_ENCODING))
         self.main_type, sep, self.sub_type = self.full_type.partition('/')
 
     def match(self, other):
diff --git a/tests/test_negotiation.py b/tests/test_negotiation.py
index 6b8fd5060..e5b9edd46 100644
--- a/tests/test_negotiation.py
+++ b/tests/test_negotiation.py
@@ -6,6 +6,7 @@ from rest_framework.negotiation import DefaultContentNegotiation
 from rest_framework.renderers import BaseRenderer
 from rest_framework.request import Request
 from rest_framework.test import APIRequestFactory
+from rest_framework.utils.mediatypes import _MediaType
 
 factory = APIRequestFactory()
 
@@ -55,3 +56,21 @@ class TestAcceptedMediaType(TestCase):
         accepted_renderer, accepted_media_type = self.select_renderer(request)
         assert accepted_media_type == 'application/openapi+json;version=2.0'
         assert accepted_renderer.format == 'swagger'
+
+    def test_match_is_false_if_main_types_not_match(self):
+        mediatype = _MediaType('test_1')
+        anoter_mediatype = _MediaType('test_2')
+        assert mediatype.match(anoter_mediatype) is False
+
+    def test_mediatype_match_is_false_if_keys_not_match(self):
+        mediatype = _MediaType(';test_param=foo')
+        another_mediatype = _MediaType(';test_param=bar')
+        assert mediatype.match(another_mediatype) is False
+
+    def test_mediatype_precedence_with_wildcard_subtype(self):
+        mediatype = _MediaType('test/*')
+        assert mediatype.precedence == 1
+
+    def test_mediatype_string_representation(self):
+        mediatype = _MediaType('test/*;foo=bar')
+        assert str(mediatype) == "test/*; foo=b'bar'"