python
diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
@@ -1827,6 +1827,7 @@ def test_HTTPError_interface(self):
     def test_gh_98778(self):
         x = urllib.error.HTTPError("url", 405, "METHOD NOT ALLOWED", None, None)
         self.assertEqual(getattr(x, "__notes__", ()), ())
+        self.assertIsInstance(x.fp.read(), bytes)
 
     def test_parse_proxy(self):
         parse_proxy_test_cases = [

diff --git a/Lib/urllib/error.py b/Lib/urllib/error.py
@@ -43,7 +43,7 @@ def __init__(self, url, code, msg, hdrs, fp):
         self.fp = fp
         self.filename = url
         if fp is None:
-            fp = io.StringIO()
+            fp = io.BytesIO()
         self.__super_init(fp, hdrs, url, code)
 
     def __str__(self):

diff --git a/Misc/ACKS b/Misc/ACKS
@@ -1897,6 +1897,7 @@ Kurt Vile
 Norman Vine
 Pauli Virtanen
 Frank Visser
+Long Vo
 Johannes Vogel
 Michael Vogt
 Radu Voicilas

diff --git a/Misc/NEWS.d/next/Library/2023-02-21-07-15-41.gh-issue-101936.QVOxHH.rst b/Misc/NEWS.d/next/Library/2023-02-21-07-15-41.gh-issue-101936.QVOxHH.rst
@@ -0,0 +1,2 @@
+The default value of ``fp`` becomes :class:`io.BytesIO` if :exc:`~urllib.error.HTTPError`
+is initialized without a designated ``fp`` parameter. Patch by Long Vo.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		The default value of ``fp`` becomes :class:`io.BytesIO` if :exc:`~urllib.error.HTTPError`
		is initialized without a designated ``fp`` parameter. Patch by Long Vo.