--- a/hgext3rd/evolve/depthcache.py	Mon Dec 18 06:48:49 2017 +0100
+++ b/hgext3rd/evolve/depthcache.py	Mon Dec 18 06:50:57 2017 +0100
@@ -5,7 +5,6 @@
 
 from mercurial import (
     localrepo,
-    node as nodemod,
     util,
     scmutil,
 )
@@ -14,10 +13,13 @@
     error,
     exthelper,
     genericcaches,
+    utility,
 )
 
 from mercurial.i18n import _
 
+filterparents = utility.filterparents
+
 eh = exthelper.exthelper()
 
 def simpledepth(repo, rev):
@@ -145,14 +147,15 @@
 
     def _depth(self, changelog, rev):
         cl = changelog
-        p1, p2 = cl.parentrevs(rev)
-        if p1 == nodemod.nullrev:
+        ps = filterparents(cl.parentrevs(rev))
+        if not ps:
             # root case
             return 1
-        elif p2 == nodemod.nullrev:
+        elif len(ps) == 1:
             # linear commit case
-            return self.get(p1) + 1
+            return self.get(ps[0]) + 1
         # merge case, must find the amount of exclusive content
+        p1, p2 = ps
         depth_p1 = self.get(p1)
         depth_p2 = self.get(p2)
         # computing depth of a merge