diff --git a/yt_dlp/__init__.py b/yt_dlp/__init__.py
index da7283300..d0d765331 100644
--- a/yt_dlp/__init__.py
+++ b/yt_dlp/__init__.py
@@ -139,10 +139,10 @@ def _real_main(argv=None):
 
     # Conflicting, missing and erroneous options
     if opts.format == 'best':
-        warnings.append('.\n         '.join(
+        warnings.append('.\n         '.join((
             '"-f best" selects the best pre-merged format which is often not the best option',
             'To let yt-dlp download and merge the best available formats, simply do not pass any format selection',
-            'If you know what you are doing and want only the best pre-merged format, use "-f b" instead to suppress this warning'))
+            'If you know what you are doing and want only the best pre-merged format, use "-f b" instead to suppress this warning')))
     if opts.usenetrc and (opts.username is not None or opts.password is not None):
         parser.error('using .netrc conflicts with giving username/password')
     if opts.password is not None and opts.username is None: