diff -up urlgrabber-3.10/urlgrabber/grabber.py.orig urlgrabber-3.10/urlgrabber/grabber.py

--- urlgrabber-3.10/urlgrabber/grabber.py.orig	2019-08-23 23:05:08.724418881 +0200

+++ urlgrabber-3.10/urlgrabber/grabber.py	2019-08-23 23:05:17.105535941 +0200

@@ -1357,7 +1357,7 @@ class PyCurlFileObject(object):

                 if buf.lower().find('content-length:') != -1:

                     length = buf.split(':')[1]

                     self.size = int(length)

-                elif self.append and self._hdr_dump == '' and ' 200 ' in buf:

+                elif self.append and self._hdr_dump == '' and ' 200 OK ' in buf:

                     # reget was attempted but server sends it all

                     # undo what we did in _build_range()

                     self.append = False