--- a/hgext/sparse.py	Fri Mar 06 10:52:44 2020 +0100
+++ b/hgext/sparse.py	Fri Mar 06 13:27:41 2020 -0500
@@ -246,7 +246,7 @@
             if changedfiles is not None:
                 # In _rebuild, these files will be deleted from the dirstate
                 # when they are not found to be in allfiles
-                dirstatefilestoremove = set(f for f in self if not matcher(f))
+                dirstatefilestoremove = {f for f in self if not matcher(f)}
                 changedfiles = dirstatefilestoremove.union(changedfiles)
 
         return orig(self, parent, allfiles, changedfiles)