diff --git a/mercurial/merge.py b/mercurial/merge.py
--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -1846,7 +1846,7 @@
             else:
                 pas = [p1.ancestor(p2, warn=branchmerge)]
 
-        fp1, fp2, xp1, xp2 = p1.node(), p2.node(), str(p1), str(p2)
+        fp1, fp2, xp1, xp2 = p1.node(), p2.node(), bytes(p1), bytes(p2)
 
         ### check phase
         if not overwrite: