diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -2759,7 +2759,7 @@
                 "`full` argument for `repo.updatecaches` is deprecated\n"
                 "(use `caches=repository.CACHE_ALL` instead)"
             )
-            self.ui.deprecwarn(msg, "5.9")
+            self.ui.deprecwarn(msg, b"5.9")
             caches = repository.CACHES_ALL
             if full == b"post-clone":
                 caches = repository.CACHES_POST_CLONE
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -1065,7 +1065,7 @@
         This method exist as `getpath` need a ui for potential warning message.
         """
         msg = b'ui.getpath is deprecated, use `get_*` functions from urlutil'
-        self.deprecwarn(msg, '6.0')
+        self.deprecwarn(msg, b'6.0')
         return self.paths.getpath(self, *args, **kwargs)
 
     @property
diff --git a/mercurial/utils/urlutil.py b/mercurial/utils/urlutil.py
--- a/mercurial/utils/urlutil.py
+++ b/mercurial/utils/urlutil.py
@@ -688,7 +688,7 @@
         path to a repo.
         """
         msg = b'getpath is deprecated, use `get_*` functions from urlutil'
-        ui.deprecwarn(msg, '6.0')
+        ui.deprecwarn(msg, b'6.0')
         # Only fall back to default if no path was requested.
         if name is None:
             if not default: