diff --git a/mercurial/upgrade.py b/mercurial/upgrade.py
--- a/mercurial/upgrade.py
+++ b/mercurial/upgrade.py
@@ -42,7 +42,7 @@
 ):
     """Upgrade a repository in place."""
     if optimize is None:
-        optimize = {}
+        optimize = set()
     repo = repo.unfiltered()
 
     specified_revlogs = {}
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
@@ -40,7 +40,6 @@
 mercurial/testing/storage.py  # tons of [attribute-error]
 mercurial/ui.py               # [attribute-error], [wrong-arg-types]
 mercurial/unionrepo.py        # ui, svfs, unfiltered [attribute-error]
-mercurial/upgrade.py          # line 84, in upgraderepo: No attribute 'discard' on Dict[nothing, nothing] [attribute-error]
 mercurial/util.py             # [attribute-error], [wrong-arg-count]
 mercurial/utils/procutil.py   # [attribute-error], [module-attr], [bad-return-type]
 mercurial/utils/stringutil.py # [module-attr], [wrong-arg-count]
@@ -88,7 +87,6 @@
   >    -x mercurial/thirdparty \
   >    -x mercurial/ui.py \
   >    -x mercurial/unionrepo.py \
-  >    -x mercurial/upgrade.py \
   >    -x mercurial/utils/procutil.py \
   >    -x mercurial/utils/stringutil.py \
   >    -x mercurial/utils/memorytop.py \