diff --git a/Lib/http/client.py b/Lib/http/client.py
--- a/Lib/http/client.py
+++ b/Lib/http/client.py
@@ -514,17 +514,17 @@ class HTTPResponse(io.RawIOBase):
                 except IncompleteRead:
                     self._close_conn()
                     raise
                 self.length = 0
             self._close_conn()        # we read everything
             return s
 
     def readinto(self, b):
-        if self.fp is None:
+        if self.fp is None or len(b) == 0:
             return 0
 
         if self._method == "HEAD":
             self._close_conn()
             return 0
 
         if self.chunked:
             return self._readinto_chunked(b)
diff --git a/Lib/test/test_httplib.py b/Lib/test/test_httplib.py
--- a/Lib/test/test_httplib.py
+++ b/Lib/test/test_httplib.py
@@ -159,16 +159,17 @@ class HeaderTests(TestCase):
 class BasicTest(TestCase):
     def test_status_lines(self):
         # Test HTTP status lines
 
         body = "HTTP/1.1 200 Ok\r\n\r\nText"
         sock = FakeSocket(body)
         resp = client.HTTPResponse(sock)
         resp.begin()
+        self.assertEqual(resp.read(0), b"")  # Issue #20007
         self.assertEqual(resp.read(), b"Text")
         self.assertTrue(resp.isclosed())
         self.assertFalse(resp.closed)
         resp.close()
         self.assertTrue(resp.closed)
 
         body = "HTTP/1.1 400.100 Not Ok\r\n\r\nText"
         sock = FakeSocket(body)