diff --git a/test/test_YoutubeDL.py b/test/test_YoutubeDL.py
index 4348cac6f..d65cc1153 100644
--- a/test/test_YoutubeDL.py
+++ b/test/test_YoutubeDL.py
@@ -714,7 +714,7 @@ def test_add_extra_info(self):
     def test_prepare_outtmpl_and_filename(self):
         def test(tmpl, expected, *, info=None, **params):
             if 'trim_file_name' not in params:
-                params['trim_file_name'] = 0  # disable trimming
+                params['trim_file_name'] = 'notrim'  # disable trimming
             params['outtmpl'] = tmpl
             ydl = FakeYDL(params)
             ydl._num_downloads = 1
@@ -935,7 +935,7 @@ def gen():
         test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='11b', filesystem_encoding='utf-8')
         test('%(title6)s.%(ext)s', 'あ' * 4 + '.mp4', trim_file_name='12b', filesystem_encoding='utf-8')
         test('%(title6)s.%(ext)s', 'あ' * 6 + '.mp4', trim_file_name='12b', filesystem_encoding='utf-16le')
-        test('folder/%(title6)s.%(ext)s', f'folder{os.path.sep}あああ.mp4', trim_file_name='3c')
+        test('folder/%(title6)s.%(ext)s', f'fol{os.path.sep}あああ.mp4', trim_file_name='3c')
 
     def test_format_note(self):
         ydl = YoutubeDL()
diff --git a/yt_dlp/YoutubeDL.py b/yt_dlp/YoutubeDL.py
index 72250fb34..287556075 100644
--- a/yt_dlp/YoutubeDL.py
+++ b/yt_dlp/YoutubeDL.py
@@ -267,7 +267,6 @@ class YoutubeDL:
     outtmpl_na_placeholder: Placeholder for unavailable meta fields.
     restrictfilenames: Do not allow "&" and spaces in file names
     trim_file_name:    Limit length of filename (extension excluded)
-    trim_file_name_mode: Mode of filename trimming ('c' for characters or 'b' for bytes)
     filesystem_encoding: Encoding to use when calculating filename length in bytes
     windowsfilenames:  True: Force filenames to be Windows compatible
                        False: Sanitize filenames only minimally
@@ -1439,8 +1438,13 @@ def evaluate_outtmpl(self, outtmpl, info_dict, *args, trim_filename=False, **kwa
         outtmpl = self.escape_outtmpl(outtmpl)
         filename = outtmpl % info_dict
 
-        max_file_name = self.params.get('trim_file_name')
-        mode = self.params.get('trim_file_name_mode')
+        def parse_trim_file_name(trim_file_name):
+            if trim_file_name is None or trim_file_name == 'notrim':
+                return 0, None
+            mobj = re.match(r'(?:(?P<length>\d+)(?P<mode>b|c)?|notrim)', trim_file_name)
+            return int(mobj.group('length')), mobj.group('mode') or 'c'
+
+        max_file_name, mode = parse_trim_file_name(self.params.get('trim_file_name'))
         if max_file_name == 0:
             # no maximum
             return filename + suffix
diff --git a/yt_dlp/__init__.py b/yt_dlp/__init__.py
index b22c4c1dd..69fb2c7e5 100644
--- a/yt_dlp/__init__.py
+++ b/yt_dlp/__init__.py
@@ -430,15 +430,8 @@ def metadataparser_actions(f):
     }
 
     # Other options
-    opts.trim_file_name_mode = 'c'
-    if opts.trim_file_name is not None:
-        mobj = re.match(r'(?:(?P<length>\d+)(?P<mode>b|c)?|notrim)', opts.trim_file_name)
-        validate(mobj, 'trim filenames', opts.trim_file_name)
-        if opts.trim_file_name == 'notrim':
-            opts.trim_file_name = 0
-        else:
-            opts.trim_file_name = int(mobj.group('length'))
-            opts.trim_file_name_mode = mobj.group('mode') or 'c'
+    validate_regex('trim filenames', opts.trim_file_name, r'(?:\d+[bc]?|notrim)')
+
     if opts.filesystem_encoding is not None:
         try:
             codecs.lookup(opts.filesystem_encoding)
@@ -902,7 +895,6 @@ def parse_options(argv=None):
         'max_downloads': opts.max_downloads,
         'prefer_free_formats': opts.prefer_free_formats,
         'trim_file_name': opts.trim_file_name,
-        'trim_file_name_mode': opts.trim_file_name_mode,
         'filesystem_encoding': opts.filesystem_encoding,
         'verbose': opts.verbose,
         'dump_intermediate_pages': opts.dump_intermediate_pages,