diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -266,7 +266,8 @@ def makeitemsdoc(ui, topic, doc, marker,
             continue
         text = gettext(text)
         if dedent:
-            text = textwrap.dedent(text)
+            # Abuse latin1 to use textwrap.dedent() on bytes.
+            text = textwrap.dedent(text.decode('latin1')).encode('latin1')
         lines = text.splitlines()
         doclines = [(lines[0])]
         for l in lines[1:]: