diff --git a/youtube_dl/YoutubeDL.py b/youtube_dl/YoutubeDL.py
index 4e2a74624..dec0e20e7 100755
--- a/youtube_dl/YoutubeDL.py
+++ b/youtube_dl/YoutubeDL.py
@@ -228,7 +228,7 @@ class YoutubeDL(object):
 
         if (sys.version_info >= (3,) and sys.platform != 'win32' and
                 sys.getfilesystemencoding() in ['ascii', 'ANSI_X3.4-1968']
-                and not params['restrictfilenames']):
+                and not params.get('restrictfilenames', False)):
             # On Python 3, the Unicode filesystem API will throw errors (#1474)
             self.report_warning(
                 'Assuming --restrict-filenames since file system encoding '