diff --git a/Lib/email/header.py b/Lib/email/header.py
index 0670885..2e687b7 100644
--- a/Lib/email/header.py
+++ b/Lib/email/header.py
@@ -275,7 +275,10 @@
             charset = Charset(charset)
         if not isinstance(s, str):
             input_charset = charset.input_codec or 'us-ascii'
-            s = s.decode(input_charset, errors)
+            if input_charset == _charset.UNKNOWN8BIT:
+                s = s.decode('us-ascii', 'surrogateescape')
+            else:
+                s = s.decode(input_charset, errors)
         # Ensure that the bytes we're storing can be decoded to the output
         # character set, otherwise an early error is thrown.
         output_charset = charset.output_codec or 'us-ascii'
diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
index 97a1e86..102e15b 100644
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -4182,6 +4182,21 @@
                         'Ynwp4dUEbay Auction Semiar- No Charge \uFFFD Earn Big')
         self.assertEqual(email.header.decode_header(h), [(x, 'unknown-8bit')])
 
+    def test_header_handles_binary_unknown8bit(self):
+        x = b'Ynwp4dUEbay Auction Semiar- No Charge \x96 Earn Big'
+        h = Header(x, charset=email.charset.UNKNOWN8BIT)
+        self.assertEqual(str(h),
+                        'Ynwp4dUEbay Auction Semiar- No Charge \uFFFD Earn Big')
+        self.assertEqual(email.header.decode_header(h), [(x, 'unknown-8bit')])
+
+    def test_make_header_handles_binary_unknown8bit(self):
+        x = b'Ynwp4dUEbay Auction Semiar- No Charge \x96 Earn Big'
+        h = Header(x, charset=email.charset.UNKNOWN8BIT)
+        h2 = email.header.make_header(email.header.decode_header(h))
+        self.assertEqual(str(h2),
+                        'Ynwp4dUEbay Auction Semiar- No Charge \uFFFD Earn Big')
+        self.assertEqual(email.header.decode_header(h2), [(x, 'unknown-8bit')])
+
     def test_modify_returned_list_does_not_change_header(self):
         h = Header('test')
         chunks = email.header.decode_header(h)