diff --git a/mercurial/minirst.py b/mercurial/minirst.py
--- a/mercurial/minirst.py
+++ b/mercurial/minirst.py
@@ -56,7 +56,7 @@ def replace(text, substs):
     # on strings in local encoding causes invalid byte sequences.
     utext = text.decode(encoding.encoding)
     for f, t in substs:
-        utext = utext.replace(f, t)
+        utext = utext.replace(f.decode("ascii"), t.decode("ascii"))
     return utext.encode(encoding.encoding)
 
 _blockre = re.compile(r"\n(?:\s*\n)+")