diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -354,6 +354,7 @@
 
             def onchangelog(cl, rev):
                 ctx = cl.changelogrevision(rev)
+                assert efilesset is not None  # help pytype
                 efilesset.update(ctx.files)
                 repo.register_changeset(rev, ctx)
 
@@ -531,12 +532,13 @@
             if added:
                 phases.registernew(repo, tr, targetphase, added)
             if phaseall is not None:
-                if duprevs:
-                    duprevs.extend(added)
+                duplicates = duprevs
+                if duplicates:
+                    duplicates.extend(added)
                 else:
-                    duprevs = added
-                phases.advanceboundary(repo, tr, phaseall, [], revs=duprevs)
-                duprevs = []
+                    duplicates = added
+                phases.advanceboundary(repo, tr, phaseall, [], revs=duplicates)
+                duprevs = duplicates = []
 
             if changesets > 0:
 
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 @@
 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 @@
 
   $ 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 \