diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -98,6 +98,9 @@
         self._ctx = ctx
         self._f = f
 
+    def __bytes__(self):
+        return b'absent file %s@%s' % (self._f, self._ctx)
+
     def path(self):
         return self._f