diff --git a/youtube_dl/downloader/external.py b/youtube_dl/downloader/external.py
index edf85483b..a4fdf1af8 100644
--- a/youtube_dl/downloader/external.py
+++ b/youtube_dl/downloader/external.py
@@ -175,7 +175,7 @@ def _call_downloader(self, tmpfilename, info_dict):
 
         args = [ffpp.executable, '-y']
 
-        start_time = info_dict.get('start_time', 0)
+        start_time = info_dict.get('start_time') or 0
         if start_time:
             args += ['-ss', compat_str(start_time)]
         end_time = info_dict.get('end_time')