diff -r 38291d9c8c1c -r 91690473856c mercurial/merge.py
--- a/mercurial/merge.py	Wed Nov 22 00:53:56 2006 +0200
+++ b/mercurial/merge.py	Thu Nov 23 22:45:00 2006 -0800
@@ -195,7 +195,7 @@
         repo.ui.debug(" %s: %s -> %s\n" % (f, msg, m))
         action.append((f, m) + args)
 
-    if not (backwards or overwrite):
+    if pa and not (backwards or overwrite):
         copy = findcopies(repo, m1, m2, ma, pa.rev())
 
     # Compare manifests