--- a/hgext3rd/evolve/stablerange.py	Sun Dec 10 04:57:19 2017 +0100
+++ b/hgext3rd/evolve/stablerange.py	Sun Dec 10 05:17:04 2017 +0100
@@ -312,6 +312,7 @@
         return self.depthrev(repo, headrev) - index
 
     def subranges(self, repo, rangeid):
+        assert 0 <= rangeid[1] <= rangeid[0], rangeid
         cached = self._getsub(rangeid)
         if cached is not None:
             return cached