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