diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -350,10 +350,11 @@ class cg1unpacker(object):
 
             def ondupchangelog(cl, rev):
                 if rev < clstart:
-                    duprevs.append(rev)
+                    duprevs.append(rev)  # pytype: disable=attribute-error
 
             def onchangelog(cl, rev):
                 ctx = cl.changelogrevision(rev)
+                assert efilesset is not None  # help pytype
                 efilesset.update(ctx.files)
                 repo.register_changeset(rev, ctx)
 
diff --git a/tests/test-check-pytype.t b/tests/test-check-pytype.t
--- a/tests/test-check-pytype.t
+++ b/tests/test-check-pytype.t
@@ -10,7 +10,6 @@ endeavor to empty this list out over tim
 probably hiding real problems.
 
 mercurial/bundlerepo.py       # no vfs and ui attrs on bundlerepo
-mercurial/changegroup.py      # mysterious incorrect type detection
 mercurial/chgserver.py        # [attribute-error]
 mercurial/cmdutil.py          # No attribute 'markcopied' on mercurial.context.filectx [attribute-error]
 mercurial/context.py          # many [attribute-error]
@@ -56,7 +55,6 @@ development, but may be a hinderance for
 
   $ pytype -V 3.6 --keep-going --jobs auto mercurial \
   >    -x mercurial/bundlerepo.py \
-  >    -x mercurial/changegroup.py \
   >    -x mercurial/chgserver.py \
   >    -x mercurial/cmdutil.py \
   >    -x mercurial/context.py \