diff -r 83f037acf71a -r 835aafb2543f mercurial/revlog.py
--- a/mercurial/revlog.py	Sun Jan 31 23:34:59 2021 +0530
+++ b/mercurial/revlog.py	Sun Jan 31 23:38:31 2021 +0530
@@ -448,14 +448,9 @@
         self.datafile = datafile or (indexfile[:-2] + b".d")
         self.nodemap_file = None
         if persistentnodemap:
-            if indexfile.endswith(b'.a'):
-                pending_path = indexfile[:-4] + b".n.a"
-                if opener.exists(pending_path):
-                    self.nodemap_file = pending_path
-                else:
-                    self.nodemap_file = indexfile[:-4] + b".n"
-            else:
-                self.nodemap_file = indexfile[:-2] + b".n"
+            self.nodemap_file = nodemaputil.get_nodemap_file(
+                opener, self.indexfile
+            )
 
         self.opener = opener
         #  When True, indexfile is opened with checkambig=True at writing, to