--- a/mercurial/subrepo.py	Thu Mar 11 18:45:18 2021 -0500
+++ b/mercurial/subrepo.py	Thu Mar 11 19:21:58 2021 -0500
@@ -1876,7 +1876,12 @@
             if info.issym():
                 data = info.linkname
             else:
-                data = tar.extractfile(info).read()
+                f = tar.extractfile(info)
+                if f:
+                    data = f.read()
+                else:
+                    self.ui.warn(_(b'skipping "%s" (unknown type)') % bname)
+                    continue
             archiver.addfile(prefix + bname, info.mode, info.issym(), data)
             total += 1
             progress.increment()