diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index 942f76d24..8bc78d0f2 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -68,6 +68,8 @@ ENGLISH_MONTH_NAMES = [
     'January', 'February', 'March', 'April', 'May', 'June',
     'July', 'August', 'September', 'October', 'November', 'December']
 
+function_pool = {}
+
 
 def preferredencoding():
     """Get preferred encoding.