diff -r fd4a38bd7e49 -r b73eb98c0243 hgext/rebase.py
--- a/hgext/rebase.py	Wed Oct 14 23:42:15 2015 +0100
+++ b/hgext/rebase.py	Thu Oct 15 00:32:20 2015 +0100
@@ -1167,7 +1167,10 @@
         if n.obsolete():
             node = cl.node(r)
             for s in obsolete.allsuccessors(repo.obsstore, [node]):
-                allsuccessors[cl.rev(s)] = cl.rev(node)
+                try:
+                    allsuccessors[cl.rev(s)] = cl.rev(node)
+                except LookupError:
+                    pass
 
     if allsuccessors:
         # Look for successors of obsolete nodes to be rebased among