diff -r ef771d329961 -r d32e7ed81f4f mercurial/revlogutils/nodemap.py
--- a/mercurial/revlogutils/nodemap.py	Sun Jan 17 02:50:26 2021 -0500
+++ b/mercurial/revlogutils/nodemap.py	Sun Jan 17 19:22:30 2021 +0100
@@ -56,7 +56,7 @@
                 data = util.buffer(util.mmapread(fd, data_length))
             else:
                 data = fd.read(data_length)
-    except OSError as e:
+    except (IOError, OSError) as e:
         if e.errno == errno.ENOENT:
             return None
         else: