--- a/hgext3rd/evolve/obsdiscovery.py	Wed Mar 22 18:36:37 2017 +0100
+++ b/hgext3rd/evolve/obsdiscovery.py	Wed Mar 22 18:37:11 2017 +0100
@@ -419,7 +419,7 @@
         return obshash
     pieces = []
     nullid = node.nullid
-    if len(rangeid) == 1:
+    if repo.stablerange.rangelength(repo, rangeid) == 1:
         rangenode = cl.node(rangeid[0])
         tmarkers = repo.obsstore.relevantmarkers([rangenode])
         pieces = []