diff --git a/mercurial/error.py b/mercurial/error.py
--- a/mercurial/error.py
+++ b/mercurial/error.py
@@ -498,8 +498,7 @@ class UnknownVersion(Abort):
 
 class LockError(IOError):
     def __init__(self, errno, strerror, filename, desc):
-        # TODO: figure out if this should be bytes or str
-        # _type: (int, str, str, bytes) -> None
+        # _type: (int, str, bytes, bytes) -> None
         IOError.__init__(self, errno, strerror, filename)
         self.desc = desc
 
@@ -508,7 +507,7 @@ class LockError(IOError):
 
 class LockHeld(LockError):
     def __init__(self, errno, filename, desc, locker):
-        LockError.__init__(self, errno, b'Lock held', filename, desc)
+        LockError.__init__(self, errno, 'Lock held', filename, desc)
         self.locker = locker
 
 
diff --git a/mercurial/lock.py b/mercurial/lock.py
--- a/mercurial/lock.py
+++ b/mercurial/lock.py
@@ -12,6 +12,7 @@ import os
 import signal
 import socket
 import time
+import typing
 import warnings
 
 from .i18n import _
@@ -154,8 +155,12 @@ def trylock(ui, vfs, lockname, timeout, 
             if delay == warningidx:
                 printwarning(ui.warn, inst.locker)
             if timeout <= delay:
+                assert isinstance(inst.filename, bytes)
                 raise error.LockHeld(
-                    errno.ETIMEDOUT, inst.filename, l.desc, inst.locker
+                    errno.ETIMEDOUT,
+                    typing.cast(bytes, inst.filename),
+                    l.desc,
+                    inst.locker,
                 )
             time.sleep(1)
             delay += 1
@@ -290,8 +295,13 @@ class lock:
                             locker,
                         )
                 else:
+                    assert isinstance(why.filename, bytes)
+                    assert isinstance(why.strerror, str)
                     raise error.LockUnavailable(
-                        why.errno, why.strerror, why.filename, self.desc
+                        why.errno,
+                        why.strerror,
+                        typing.cast(bytes, why.filename),
+                        self.desc,
                     )
 
         if not self.held:
diff --git a/mercurial/statichttprepo.py b/mercurial/statichttprepo.py
--- a/mercurial/statichttprepo.py
+++ b/mercurial/statichttprepo.py
@@ -243,7 +243,7 @@ class statichttprepository(
     def wlock(self, wait=True):
         raise error.LockUnavailable(
             0,
-            _(b'lock not available'),
+            pycompat.sysstr(_(b'lock not available')),
             b'lock',
             _(b'cannot lock static-http repository'),
         )
@@ -251,7 +251,7 @@ class statichttprepository(
     def lock(self, wait=True):
         raise error.LockUnavailable(
             0,
-            _(b'lock not available'),
+            pycompat.sysstr(_(b'lock not available')),
             b'lock',
             _(b'cannot lock static-http repository'),
         )