diff --git a/hgext/convert/common.py b/hgext/convert/common.py
--- a/hgext/convert/common.py
+++ b/hgext/convert/common.py
@@ -72,8 +72,10 @@ class _shlexpy3proxy:
         return _encodeornone(self._l.get_token())
 
     @property
-    def infile(self):
-        return self._l.infile or b'<unknown>'
+    def infile(self) -> bytes:
+        if self._l.infile is not None:
+            return encoding.strtolocal(self._l.infile)
+        return b'<unknown>'
 
     @property
     def lineno(self) -> int:
@@ -82,7 +84,7 @@ class _shlexpy3proxy:
 
 def shlexer(
     data=None,
-    filepath: Optional[str] = None,
+    filepath: Optional[bytes] = None,
     wordchars: Optional[bytes] = None,
     whitespace: Optional[bytes] = None,
 ):
@@ -94,7 +96,8 @@ def shlexer(
                 b'shlexer only accepts data or filepath, not both'
             )
         data = data.decode('latin1')
-    l = shlex.shlex(data, infile=filepath, posix=True)
+    infile = encoding.strfromlocal(filepath) if filepath is not None else None
+    l = shlex.shlex(data, infile=infile, posix=True)
     if whitespace is not None:
         l.whitespace_split = True
         l.whitespace += whitespace.decode('latin1')
diff --git a/hgext/convert/filemap.py b/hgext/convert/filemap.py
--- a/hgext/convert/filemap.py
+++ b/hgext/convert/filemap.py
@@ -76,7 +76,7 @@ class filemapper:
     rename: MutableMapping[bytes, bytes]
     targetprefixes: Optional[Set[bytes]]
 
-    def __init__(self, ui: "uimod.ui", path=None) -> None:
+    def __init__(self, ui: "uimod.ui", path: Optional[bytes] = None) -> None:
         self.ui = ui
         self.include = {}
         self.exclude = {}
@@ -86,8 +86,7 @@ class filemapper:
             if self.parse(path):
                 raise error.Abort(_(b'errors in filemap'))
 
-    # TODO: cmd==b'source' case breaks if ``path``is str
-    def parse(self, path) -> int:
+    def parse(self, path: Optional[bytes]) -> int:
         errs = 0
 
         def check(name: bytes, mapping, listname: bytes):
@@ -218,7 +217,9 @@ class filemapper:
 
 
 class filemap_source(common.converter_source):
-    def __init__(self, ui: "uimod.ui", baseconverter, filemap) -> None:
+    def __init__(
+        self, ui: "uimod.ui", baseconverter, filemap: Optional[bytes]
+    ) -> None:
         super(filemap_source, self).__init__(ui, baseconverter.repotype)
         self.base = baseconverter
         self.filemapper = filemapper(ui, filemap)