diff -r 40ace21cb3a1 -r 12312f066d93 mercurial/commands.py
--- a/mercurial/commands.py	Thu Apr 17 20:01:35 2014 +0200
+++ b/mercurial/commands.py	Thu Apr 17 20:01:39 2014 +0200
@@ -438,7 +438,7 @@
     node = scmutil.revsingle(repo, rev).node()
 
     op1, op2 = repo.dirstate.parents()
-    if node not in repo.changelog.commonancestors(op1, node):
+    if node not in repo.changelog.commonancestorsheads(op1, node):
         raise util.Abort(_('cannot backout change that is not an ancestor'))
 
     p1, p2 = repo.changelog.parents(node)