diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -246,7 +246,6 @@
         return {}
 
     repo = a.repo().unfiltered()
-    children = {}
 
     cl = repo.changelog
     isancestor = cl.isancestorrev