--- a/hgext/narrow/narrowspec.py	Mon Feb 12 14:27:32 2018 -0500
+++ b/hgext/narrow/narrowspec.py	Mon Feb 12 14:37:10 2018 -0500
@@ -180,7 +180,7 @@
     >>> restrictpatterns({'f1/$non_exitent_var'}, {}, ['f1','f2'], [])
     (set(['f1/$non_exitent_var']), {})
     """
-    res_excludes = req_excludes.copy()
+    res_excludes = set(req_excludes)
     res_excludes.update(repo_excludes)
     if not req_includes:
         res_includes = set(repo_includes)