diff --git a/test/test_YoutubeDL.py b/test/test_YoutubeDL.py
index 8da1e5e4b..49ae9e2b1 100644
--- a/test/test_YoutubeDL.py
+++ b/test/test_YoutubeDL.py
@@ -822,6 +822,7 @@ class TestYoutubeDL(unittest.TestCase):
         test('%(title&foo|baz)s.bar', 'baz.bar')
         test('%(x,id&foo|baz)s.bar', 'foo.bar')
         test('%(x,title&foo|baz)s.bar', 'baz.bar')
+        test('%(title&\n|)s', '\n')
 
         # Laziness
         def gen():
diff --git a/yt_dlp/YoutubeDL.py b/yt_dlp/YoutubeDL.py
index 31f7645dc..61c149e47 100644
--- a/yt_dlp/YoutubeDL.py
+++ b/yt_dlp/YoutubeDL.py
@@ -1156,7 +1156,7 @@ class YoutubeDL:
         }
         MATH_FIELD_RE = rf'(?:{FIELD_RE}|-?{NUMBER_RE})'
         MATH_OPERATORS_RE = r'(?:%s)' % '|'.join(map(re.escape, MATH_FUNCTIONS.keys()))
-        INTERNAL_FORMAT_RE = re.compile(rf'''(?x)
+        INTERNAL_FORMAT_RE = re.compile(rf'''(?xs)
             (?P<negate>-)?
             (?P<fields>{FIELD_RE})
             (?P<maths>(?:{MATH_OPERATORS_RE}{MATH_FIELD_RE})*)
diff --git a/yt_dlp/options.py b/yt_dlp/options.py
index 84aeda7f1..d334a9caa 100644
--- a/yt_dlp/options.py
+++ b/yt_dlp/options.py
@@ -243,7 +243,7 @@ def create_parser():
         if multiple_keys:
             allowed_keys = fr'({allowed_keys})(,({allowed_keys}))*'
         mobj = re.match(
-            fr'(?i)(?P<keys>{allowed_keys}){delimiter}(?P<val>.*)$',
+            fr'(?is)(?P<keys>{allowed_keys}){delimiter}(?P<val>.*)$',
             value[0] if multiple_args else value)
         if mobj is not None:
             keys, val = mobj.group('keys').split(','), mobj.group('val')