diff --git a/test/test_YoutubeDL.py b/test/test_YoutubeDL.py
index 58cf9c3136..3100c362aa 100644
--- a/test/test_YoutubeDL.py
+++ b/test/test_YoutubeDL.py
@@ -7,6 +7,7 @@ import unittest
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
 from test.helper import FakeYDL
+from youtube_dl import YoutubeDL
 
 
 class YDL(FakeYDL):
@@ -140,6 +141,20 @@ class TestFormatSelection(unittest.TestCase):
         self.assertEqual(test_dict['extractor'], 'Foo')
         self.assertEqual(test_dict['playlist'], 'funny videos')
 
+    def test_prepare_filename(self):
+        info = {
+            u'id': u'1234',
+            u'ext': u'mp4',
+            u'width': None,
+        }
+        def fname(templ):
+            ydl = YoutubeDL({'outtmpl': templ})
+            return ydl.prepare_filename(info)
+        self.assertEqual(fname(u'%(id)s.%(ext)s'), u'1234.mp4')
+        self.assertEqual(fname(u'%(id)s-%(width)s.%(ext)s'), u'1234-NA.mp4')
+        # Replace missing fields with 'NA'
+        self.assertEqual(fname(u'%(uploader_date)s-%(id)s.%(ext)s'), u'NA-1234.mp4')
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/youtube_dl/YoutubeDL.py b/youtube_dl/YoutubeDL.py
index 2dd7e49071..11d4972dd6 100644
--- a/youtube_dl/YoutubeDL.py
+++ b/youtube_dl/YoutubeDL.py
@@ -3,6 +3,7 @@
 
 from __future__ import absolute_import
 
+import collections
 import errno
 import io
 import json
@@ -401,13 +402,11 @@ class YoutubeDL(object):
                 is_id=(k == u'id'))
             template_dict = dict((k, sanitize(k, v))
                                  for k, v in template_dict.items())
+            template_dict = collections.defaultdict(lambda: u'NA', template_dict)
 
             tmpl = os.path.expanduser(self.params['outtmpl'])
             filename = tmpl % template_dict
             return filename
-        except KeyError as err:
-            self.report_error(u'Erroneous output template')
-            return None
         except ValueError as err:
             self.report_error(u'Error in output template: ' + str(err) + u' (encoding: ' + repr(preferredencoding()) + ')')
             return None