--- a/hgext3rd/evolve/stablerange.py	Wed Mar 22 18:40:54 2017 +0100
+++ b/hgext3rd/evolve/stablerange.py	Wed Mar 22 18:41:26 2017 +0100
@@ -343,7 +343,7 @@
         self._head = head
         self._index = index
         if revs is not None:
-            assert len(revs) == len(self)
+            assert len(revs) == self._len()
             self._revs = revs
         assert index < self.depth, (head, index, self.depth, revs)
 
@@ -376,8 +376,8 @@
     def _stablekey(self):
         return (self[0], self[1])
 
-    def __len__(self):
-        return self.depth - self[1]
+    def _len(self):
+        return self._repo.stablerange.rangelength(self._repo, self)
 
     @util.propertycache
     def depth(self):
@@ -386,7 +386,7 @@
     @util.propertycache
     def _revs(self):
         r = stablesort(self._repo, [self[0]])[self[1]:]
-        assert len(r) == len(self), (self[0], self[1], len(r), len(self))
+        assert len(r) == self._len(), (self[0], self[1], len(r), self._len())
         return r
 
     def subranges(self):