diff --git a/acme/acme/jose/b64.py b/acme/acme/jose/b64.py
index 5fccdce2e..cf79aa820 100644
--- a/acme/acme/jose/b64.py
+++ b/acme/acme/jose/b64.py
@@ -22,7 +22,7 @@ def b64encode(data):
     """JOSE Base64 encode.
 
     :param data: Data to be encoded.
-    :type data: `bytes` or `bytearray`
+    :type data: `bytes`
 
     :returns: JOSE Base64 string.
     :rtype: bytes
@@ -30,9 +30,8 @@ def b64encode(data):
     :raises TypeError: if `data` is of incorrect type
 
     """
-    if not isinstance(data, (six.binary_type, bytearray)):
-        raise TypeError('argument should be {0} or bytearray'.format(
-            six.binary_type))
+    if not isinstance(data, six.binary_type):
+        raise TypeError('argument should be {0}'.format(six.binary_type))
     return base64.urlsafe_b64encode(data).rstrip(b'=')
 
 
diff --git a/acme/acme/jose/b64_test.py b/acme/acme/jose/b64_test.py
index 989f8e7fe..cbabe2251 100644
--- a/acme/acme/jose/b64_test.py
+++ b/acme/acme/jose/b64_test.py
@@ -39,9 +39,6 @@ class B64EncodeTest(unittest.TestCase):
         for text, (b64, _) in six.iteritems(B64_PADDING_EXAMPLES):
             self.assertEqual(self._call(text), b64)
 
-    def test_bytearray_ok(self):
-        self.assertEqual(self._call(bytearray(b'foo')), b'Zm9v')
-
     def test_unicode_fails_with_type_error(self):
         self.assertRaises(TypeError, self._call, u'some unicode')