diff --git a/youtube_dl/YoutubeDL.py b/youtube_dl/YoutubeDL.py
index d69cd32f8..47c52d520 100755
--- a/youtube_dl/YoutubeDL.py
+++ b/youtube_dl/YoutubeDL.py
@@ -110,7 +110,7 @@ class _NA_formatter(object):
     to prevent stuff such as {upload_date:%Y} from yielding errors"""
     def __format__(self, fmt):
         return 'NA'
-    def __str__(self, fmt):
+    def __str__(self):
         return 'NA'  # just in case; can probably be removed