--- a/hgext/rebase.py	Thu Nov 18 19:52:58 2010 -0200
+++ b/hgext/rebase.py	Sat Nov 20 09:51:56 2010 +0100
@@ -485,7 +485,7 @@
             srcancestors = set(repo.changelog.ancestors(source))
             baseancestors = set(repo.changelog.ancestors(commonbase.rev()))
             detachset = srcancestors - baseancestors
-            detachset.remove(commonbase.rev())
+            detachset.discard(commonbase.rev())
     else:
         if base:
             cwd = repo[base].rev()