diff --git a/yt_dlp/YoutubeDL.py b/yt_dlp/YoutubeDL.py
index ada870c48..8432abf1a 100644
--- a/yt_dlp/YoutubeDL.py
+++ b/yt_dlp/YoutubeDL.py
@@ -2750,7 +2750,7 @@ class YoutubeDL(object):
                     _protocols = set(determine_protocol(f) for f in requested_formats)
                     if len(_protocols) == 1:  # All requested formats have same protocol
                         info_dict['protocol'] = _protocols.pop()
-                    directly_mergable = FFmpegFD.can_merge_formats(info_dict)
+                    directly_mergable = FFmpegFD.can_merge_formats(info_dict, self.params)
                     if dl_filename is not None:
                         self.report_file_already_downloaded(dl_filename)
                     elif (directly_mergable and get_suitable_downloader(
diff --git a/yt_dlp/downloader/external.py b/yt_dlp/downloader/external.py
index 3dddedb14..9db248df4 100644
--- a/yt_dlp/downloader/external.py
+++ b/yt_dlp/downloader/external.py
@@ -357,7 +357,7 @@ class FFmpegFD(ExternalFD):
         pass
 
     @classmethod
-    def can_merge_formats(cls, info_dict, params={}):
+    def can_merge_formats(cls, info_dict, params):
         return (
             info_dict.get('requested_formats')
             and info_dict.get('protocol')