--- a/mercurial/exchangev2.py	Fri Nov 08 16:00:47 2019 +0100
+++ b/mercurial/exchangev2.py	Fri Nov 08 13:25:25 2019 +0100
@@ -291,9 +291,9 @@
     # See the comment in exchange._pulldiscoverychangegroup() for more.
 
     if fetch and remoteheads:
-        nodemap = repo.unfiltered().changelog.nodemap
+        has_node = repo.unfiltered().changelog.index.has_node
 
-        common |= {head for head in remoteheads if head in nodemap}
+        common |= {head for head in remoteheads if has_node(head)}
 
         if set(remoteheads).issubset(common):
             fetch = []