diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -733,7 +733,7 @@
 
     repo = repo.unfiltered()
     cl = repo.changelog
-    rev = cl.nodemap.get
+    rev = cl.index.get_rev
     if not roots:
         return heads
     if not heads or heads == [nullid]: