diff --git a/Lib/email/header.py b/Lib/email/header.py
index 0a66df54ae6..06708853c2d 100644
--- a/Lib/email/header.py
+++ b/Lib/email/header.py
@@ -73,9 +73,10 @@ def decode_header(header):
     An email.errors.HeaderParseError may be raised when certain decoding error
     occurs (e.g. a base64 decoding exception).
     """
-    # If it is a Header object, we can just return the chunks.
+    # If it is a Header object, we can just return the encoded chunks.
     if hasattr(header, '_chunks'):
-        return list(header._chunks)
+        return [(_charset._encode(string, str(charset)), str(charset))
+                    for string, charset in header._chunks]
     # If no encoding, just return the header with no charset.
     if not ecre.search(header):
         return [(header, None)]
diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
index 281a65a6da4..97a1e86a25f 100644
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -4176,8 +4176,8 @@ def test_bad_8bit_header(self):
 
     def test_escaped_8bit_header(self):
         x = b'Ynwp4dUEbay Auction Semiar- No Charge \x96 Earn Big'
-        x = x.decode('ascii', 'surrogateescape')
-        h = Header(x, charset=email.charset.UNKNOWN8BIT)
+        e = x.decode('ascii', 'surrogateescape')
+        h = Header(e, 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')])
diff --git a/Misc/NEWS b/Misc/NEWS
index 170d5224d96..9c3f69347e5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -25,6 +25,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #11584: email.header.decode_header no longer fails if the header
+  passed to it is a Header object.
+
 - Issue #11700: mailbox proxy object close methods can now be called multiple
   times without error.