--- a/hgext3rd/evolve/stablerange.py
+++ b/hgext3rd/evolve/stablerange.py
@@ -391,25 +391,24 @@
         p1, p2 = self._parents(rangeid[0], repo.changelog.parentrevs)
         if p2 != nodemod.nullrev:
             return self._slicesrangeatmerge(repo, rangeid, globalindex)
-        assert p1 != nodemod.nullrev
-        rangedepth = self.depthrev(repo, rangeid[0])
-        topsize = rangedepth - globalindex
+
+        reuserev = p1
 
-        parentrange = (p1, rangeid[1])
+        assert reuserev != nodemod.nullrev
+
+        reuserange = (reuserev, rangeid[1])
+        top = (rangeid[0], globalindex)
 
-        if topsize == 1:
-            top = (rangeid[0], globalindex)
-            return [parentrange, top]
-        else:
-            # This will not initiate a recursion since we took appropriate
-            # precaution in the caller of this method to ensure it will be so.
-            # It the parent is a merge that will not be the case but computing
-            # subranges from a merge will not recurse.
-            parentsubranges = self.subranges(repo, parentrange)
-            slices = parentsubranges[:-1] # pop the top
-            top = (rangeid[0], globalindex)
-            slices.append(top)
-            return slices
+        if rangeid[1] + self.rangelength(repo, reuserange) == globalindex:
+            return [reuserange, top]
+        # This will not initiate a recursion since we took appropriate
+        # precaution in the caller of this method to ensure it will be so.
+        # It the parent is a merge that will not be the case but computing
+        # subranges from a merge will not recurse.
+        reusesubranges = self.subranges(repo, reuserange)
+        slices = reusesubranges[:-1] # pop the top
+        slices.append(top)
+        return slices
 
     def _slicesrangeatmerge(self, repo, rangeid, globalindex):
         localindex = globalindex - rangeid[1]